>why does marriage have to be between a man and a women?

You're misunderstanding me. I think gay people should be allowed to marry. I was illustrating the rationale behind proposition 8. Its supporters knew that they didn't have the support that was needed in order to outright ban homosexual unions, and so they wanted to at least prevent them from calling those unions 'marriages'. If they were successful in excluding homosexual relationships from their constitutional definition of marriage, then they would have successfully forced homosexuals to call their marriages something else.

I am not saying I agree with this, but allowing gay people to be married gives them rights to adopt children. If you believe that the foundation of society is traditional family and that children should be raised, when possible, in a traditional family, you could see why someone would appose gay marriage.