If there are no legitimate reasons to ban gay marriage then exactly what reason is there for denying 3 or 4 people the right to marry each other? I mean if the only criteria, as was stated by gays as consenting adults and love, you haven't a leg to stand on.
No class of persons is adversely effected, no suspect class of persons is being discriminated against, as laws prohibiting plural marriage apply equally to everyone.
That’s not the case with laws denying same-sex couples their equal protection rights, as such laws exist only to make same-sex couples different from everyone else. This a state cannot do, ‘a state cannot so deem a class of persons a stranger to its laws,’ including marriage law. See:
Romer v. Evans (1996).
And those seeking to enter into a plural marriage do not constitute a ‘class of persons,’ nor are they a ‘suspect class’ for reasons of judicial review.