Here we see the validity of the Supreme Court majority’s concerns in Slaughter-House about the vagueness of the 14th Amendment. All legislation classifies, and thus treats people differently. If we understand the Equal Protection Clause as divorced from the concerns that yielded it, we elevate the Supreme Court to the position of Grand Censor of American Legislation. Since 1954, that has been the direction in which federal courts have headed.
As I understand it, the argument is tantamount to saying that allowing women to marry men while disallowing men to do so is iniquitously to deny those men equal protection. The problem is that we have no way of saying where this principle should cease to be applied, and so all we can do is gaze on in wonder as The Nine work their will.
It must be facetious to ask what this means regarding federalism. Truly.