All of this is known as "tiered" scrutiny, and it has had many critics, including Justice Thurgood Marshall who argued for a "spectrum of standards in reviewing discrimination", instead of discrete tiers. Justice John Paul Stevens argued for only one level of scrutiny, given that "there is only one Equal Protection Clause".Fleming, James. "'There is Only One Equal Protection Clause': An Appreciation of Justice Stevens's Equal Protection Jurisprudence", Fordham Law Review, Vol. 74, p. 2301, 2306 (2006). The whole tiered strategy developed by the Court is meant to reconcile the principle of equal protection with the reality that most laws necessarily discriminate in some way.See Romer v. Evans, 517 U.S. 620, 631 (1996): "the equal protection of the laws must coexist with the practical necessity that most legislation classifies for one purpose or another, with resulting disadvantage to various groups or persons."
