Not every heterosexual wants this kind of relationship. Not every homosexual does either. But those who do deserve the best that marriage can offer. So yes . . . marriage through the '90s was darkly tarnished. But denying marriage to gay men, lesbians, bisexuals and transgendered people will not untarnish it.
Heterosexuals have to take responsibility for the mess they've made of marriage.
They were the ones who wanted to have marriage. Now, in the ultimate paradox, heterosexuals may actually need the help of homosexuals, if they want to put some sacredness back in marriage.