with whom SPOTTSWOOD W. ROBINSON, III, Circuit Judge, joins, concurring in the denial of rehearing en banc:
The Chief Judge offers two justifications to slip Chevron’s restraining leash. Neither is grounded on an actual construction of the statutory language (which she concedes is ambiguous) nor its legislative history. Instead, the Chief Judge first interposes a theoretical economic argument to challenge the reasonableness of the Attorney General’s interpretation of the statute. The Attorney General’s conclusion that the Detroit Free Press is in “probable danger of financial failure” is unreasonable, we are told, because it is based on an economically unreasonable prediction — that the Detroit News is willing to continue to price below its costs in order to drive the Free Press to close its doors.1 This is unreasonable because sophisticated firms do not— over a significant period of time — cut prices in order to drive a competitor out of the market, unless entry barriers prevent new competitors from emerging. If new competitors could emerge, the costs incurred in driving the old competitor out of the market would be wasted. See Cargill, Inc. v. Monfort of Colorado, Inc., 479 U.S. 104, 121 n. 17, 107 S.Ct. 484, 495 n. 17, 93 L.Ed.2d 427 (1986); Matsushita Electric Industrial Co. v. Zenith Radio Corp., 475 U.S. 574, 589, 106 S.Ct. 1348, 1357, 89 L.Ed.2d 538 (1986).
I quite agree with that proposition. But I cannot see its relevance to this case. Congress obviously would not have passed the Newspaper Preservation Act unless it had perceived entry barriers that prevented an effective challenge to a monopoly newspaper. And, although it is not up to us to question Congress’ judgment, surely we have seen nothing in this case to suggest Congress was misinformed. Whether those entry barriers, as a theoretical matter, are properly analyzed as due to a natural monopoly2 or a variation on that classic *1302economic theme (I am beginning to doubt that anyone truly understands the newspaper market) is beside the point. Congress authorized the Attorney General to prevent a city newspaper editorial monopoly — even at the risk of a shared economic monopoly —because it thought the unusual economics of the newspaper industry compelled that exception to the antitrust laws. Otherwise, one newspaper may achieve a stunning fusion of economic and editorial (political) power due to the loss of actual and potential competition. The Chief Judge’s basic quarrel thus is with the premise of the statute itself.
Although the appellants did not present the theoretical gloss that the Chief Judge puts on their argument, they did rely — as does the Chief Judge — on the Attorney General’s statement that hypothetically Detroit could support both papers. That would be so if — and this is a big if — both papers raised their prices. The Attorney General, however, never predicted how long that hypothetical situation would last or how it might be enforced.3 There is the rub. As Congress realized, see S.Rep. No. 535, 91st Cong., 1st Sess. 2-4 (1969), one of the competing newspapers in any American city seems all too often to achieve a dominant position, which means that a newspaper owner who holds an advantage in a two newspaper city might be irrational if he did not attempt to drive his competitor out of business. Otherwise, he might wake up one day to realize that he had lost the superior position and was already himself in the downward spiral. In other words, an unregulated long-term two newspaper corn-petitive equilibrium may well be a rarity (if not a chimera), and surely no newspaper owner in such a market can be confident that he and his competitor are in that exceptional city. See 116 Cong.Rec. 1788 (1970) (Statement of Sen. Fong) (“[I]t [is] increasingly difficult for many newspapers to coexist in the same community under conditions of all-out economic competition.”). Accordingly, the AU found that the “strategies pursued by the Free Press and News ... were perceived by management as economically rational given the history of the demise of junior papers which had entered the downward spiral.” AU Report, at 112-13. Even if the Detroit market was an exception to the prevailing pattern, the News (and the Free Press) could not possibly know that, and therefore neither paper would rationally gamble on such an assumption.
I do not see, in short, how the Chief Judge’s interposition of economic theory supports her contention that the Attorney General’s construction of the statute or his prediction as to the Detroit News’ behavior is unreasonable.
Chief Judge Wald’s second contention (inconsistent with her first) assumes that it would be reasonable for the News to continue to price below cost in order to drive the Free Press out of business, but argues that such behavior constitutes illegal predation — or something “perilously close” to illegal predation. The difficulty with this argument, no matter how couched, is not only was it not raised by appellant in this court,4 it was not raised by any party — in-*1303eluding the antitrust division — before the ALT or the Attorney General. Indeed, the AU specifically noted that it was unnecessary to consider whether predation would affect his analysis of the statute, because it was not argued in this case. AU Report, at 122 n. 303. And he observed that competition short of predation — even that designed to drive competitors out of business —was irrelevant, since the NPA “neither penalize[s] nor reward[s] firms determined to eliminate their competition.” Id. at 122. No party specifically challenged either of those observations of the AU at any stage in these proceedings. It is, of course, black letter law that an argument not made before an agency cannot be the basis of a legal challenge on appeal. Unemployment Compensation Comm’n v. Aragon, 329 U.S. 143, 155, 67 S.Ct. 245, 251, 91 L.Ed. 136 (1946); United States v. L.A. Tucker Trucklines, 344 U.S. 33, 37, 73 S.Ct. 67, 69, 97 L.Ed. 54 (1952); Safir v. Kreps, 551 F.2d 447, 452 (D.C.Cir.1977) (“[Ajppellant is not free to raise points without regard to whether they were argued at some stage of the administrative process.”).5
Chief Judge Wald’s predation argument, moreover, implicates a good deal more than the Attorney General’s approach to Joint Operating Agreements. If the Attorney General were to conclude that he would not approve a JOA if the stronger paper had engaged in below cost pricing for some period before the submission of the JOA, he would have to assume the responsibility for preventing that “predation.” Otherwise, newspapers like the News would, for the reasons described above, engage in such behavior to achieve dominance in their markets without regard to a JOA. By suggesting that the News’ pricing practices were “illegal predation,” the Chief Judge, in other words, implicitly seeks to preempt prosecutorial decisions of the Executive Branch.
Nevertheless, the Attorney General and his Antitrust Division might ponder Chief Judge Wald’s suggested approach to newspaper antitrust enforcement policy and modify their position accordingly. Or, in a future case, a party might make the argument the Chief Judge suggests. That, however, is all the more reason to deny rehearing here. If and when we are properly faced with the contentions the Chief Judge advances, we can decide their correctness. In that event, this case might not have any enduring impact.
. Or more accurately, the question is whether the Attorney General reasonably believed that the Detroit Free Press reasonably believes that the News will follow that course. In that event, as we said in our opinion, the Free Press’ assertion that it will shut down if the JOA is denied is hardly incredible.
. See C. Kaysen & D. Turner, Antitrust Policy 191 n. 1 (1971) ("There are disturbing indications that newspaper publishing is approaching this unhappy state [of natural monopoly] in many cities and towns.”). The Attorney General never took a position on whether the Detroit market is a natural monopoly, and the passage on which the Chief Judge relies obviously fails to suggest that he did. See Statement of Chief Judge Wald, at 2 n. 2. The Attorney General simply said that "the Free Press plainly does not face external market forces — such as rising costs, competition from other media outlets and the siphoning off of readers from the metropolitan region to the suburbs — that would portend almost certain failure." And his statement that “the Detroit market could sustain two profitable newspapers if both circulations and advertising prices were increased” is not really inconsistent with the possibility that the Detroit market is a natural monopoly. See P. Areeda & D. Turner, Antitrust Law, § 621, at 48 (In a natural monopoly market, "demand may be sufficient at some price fixed by law or cartel to cover the costs of more than one producer, but the cost of production will be significantly lower with a single producer."). The ALJ did say that "there is no convincing evidence that superior scale economies is [sic] likely to be determinative for the News,” but it is by no means clear that it is only or chiefly scale economies that cause one-newspaper towns. That may be why the newspaper *1302market is so puzzling.
. The AU did quote the management of the Free Press as saying that the paper could become profitable if "competitive pricing becomes rational and consistent with other markets around the country.” See Statement of Chief Judge Wald, at 1. But, as we explained in our opinion, all the Attorney General said was that some hypothetical pricing scheme could support two papers.
. Appellants merely contended {see Statement of Chief Judge Wald, at 6 n. 7) that the Attorney General’s interpretation of the NPA would allow large corporate newspaper chains to obtain JOAs by pursuing a course of aggressive competition. Only the amicus mentioned predation, and its concern was that approval of the Detroit JOA would lead to illegal pricing in Little Rock. Amicus asserted that the Arkansas Gazette had engaged in “unprecedented” predatory action in hopes of obtaining a JOA (which suggests that Little Rock might be an appropriate place to advance the Chief Judge's argument). The ami-cus filed no public comments on the Detroit *1303JOA with the Attorney General and did not seek to intervene in that proceeding. The major Detroit-area newspaper unions and Mayor Young of Detroit did intervene before the Attorney General, see 28 C.F.R. § 48.11, but did not appeal. Moreover, appellants only barely (in one sentence) made the argument that Judge Ruth B. Ginsburg focused on in her dissent — that exceptions to the antitrust laws should be narrowly construed.
. Perhaps appellants did not raise the predation argument here because they knew it was not raised before the Attorney General.