You do bring up a valid point. I still don't necessarily believe in it based upon my religious upbringing. And according to the original definitions of marriage and what it was founded upon, homosexual marriages are contradictory. The government may have twisted the definition, but I don't think thats really a good thing.
Biologically speaking, marriage refers to opposites attracting to create life.
Religiously speaking, it refers to the union between man and woman.
People need to stop warping the definitions of certain words. What's so wrong with just calling a gay marriage a union? Yes, I understand that civil unions don't offer as many rights to the couple as marriage does. However, that's the government's fault; not the religions' faults. If anything, a reform for the rights offered in a "civil union" should be put into place, rather than the redefining of a religious term.
Biologically, homosexual activity is natural. Separate but equal failed for a reason. Why can't the government call it a marriage and allow equal opportunity, and tax breaks for it.