I support gay marriage if both chicks are hot.... lol Okay had to get that out of the way.
I think it is safe to assume MOST people are straight. That a man and a woman join to create new life to me is evidence this is the intended design of our evolution. Where I think most Hetero people fail to support the gay community is, when I am porking my wife, I might be ensuring life goes on after I am gone. The physical act of our sex has a function of the species.
Gay sex, (not sure but in hetero relationships, sex sort of seals the marriage) does not have this purpose. It is done purely for pleasure. No other reason.
I myself have had sex purely to reproduce. Sex while a female is pregnant in the last trimester also helps loosen up the canal for the baby.
I guess my question is what needs protection. I like having my wife and children protected, but if you are 2 guys or 2 girls... what is really going on? I mean just to have the piece of paper and commitment to each other? My marriage ensures I have rights to my children and they to me. I know you can adopt or for women they can artificially inseminate, I am going to say for most kids, that will bug the shit out of them not knowing who dad was. Medical history alone.
I guess my point over all is for every argument for gay marriage they all seem to fall a bit short as to why hetero couples get married. Truth be told, thats why people oppose it.