I think a lot of problems could be avoided if congress simply established a legal definition of marriage or civil unions. This can of course include homosexual folks.

Maybe something like ( and I know it is simplistic)

"A life partnership between mutually consenting adult persons". ( I actually have no real problem with multiple partner situations as long as everyone invovled is aware and consents)

This would allow gays to marry openly, while at the same time prevent people from using legalizing gay marriage as a means to promote preverted and damaging arrangments, like trying to marry a child or an animal. ( I know that is really sick, but there are some freaky people who actually try this stuff)