The problem with gay marriage is that it is re-defining the word marriage.  It is typical of the movement toward Relativism in our culture that definitions aren't really true.  Definitions, much like truth, are absolute.  They don't really adjust, they remain fundamentally the same.  Hence the definition of the word, definition.  It is definite.

Relativism is a cancer on society throwing away truth and fogging up one's ability to see the truth.  I always chuckle at those who think that all truth is relative.  All one need to ask to demonstrate the absurdity of that statement is to ask, 'is that an absolute truth?'

God defined marriage as between a man and a woman.  Any other  combination of marriage partners is a perversion of the definition of marriage.  This is not to say that there cannot be civil unions or societal contracts that afford people the legal rights of marriage in society, but please don't call it marriage.  Calling it marriage dilutes and relativizes the definition of marriage.  It takes us further down the road farther from the truth.