Basman's (an Osgoode Hall--the Best Law School in the Commonwealth--Grad) Short Note on Medved's

This post is legalistic.

The issue is not the difference between discrimination and distinction: every distinction that favours or burdens a group turns on discrimination; all discrimination turns on distinction.

The issue also is not what's legal.

The issue is the principled basis for not allowing gay marriage. As you say, this disallowance is based on gender not race. But the question is not answered by that asssertion. To rest on this assertion merely begs the question, makes your conclusion your premise.

Absent a persuasive answer to the question, anyone is right to say that to disallow an interracial couple from marrying is analogous to forbidding gay couples from marrying. Both discriminations are based on unjustifiable distinctions.