What non religious reasons are there for banning and not recognizing gay marriages?

anyone? anyone? the only one i can see is they cant have kids, which they could with a surrogate, and many heterosexual couples cannot have children either. i mean marriage is a governmental institution, not a religious one, what non religious reasons are there for denying two people equality because of their sexual orientation... it seems down right un-american to me.. and for all who cry tradition, some traditions need changing... i say this all as a straight man too they arent asking for special treatment... just equal treatment... i mean did you choose to be straight? if your religion doesnt support gay marriage... dont practice it, no one is going to force you to, marriages dont have to be preformed in a church fyi. marriage is a social and governmental institution... atheists and non religious people can get married, in fact any one from any religion or lack thereof can get married... and to all who resort to the "well what about bestiality and pedophilia and polygamy?" i say it boils down to consent... an animal cannot consent, a child cannot consent, i have no problems with polygamy between consenting adults, but i would never do it.