Those two words together always seem like a total contradiction of each other. You cannot be homosexual and married, what is the point, what is the purpose? It is selfish, purely based on desires that are contrary to what we believe. In Genesis God creates Adam and then Eve so Adam could have a helpmate, one who compliments him.
Ebeth at Pillars has some great points to make.
A Catholic Mom climbing the Pillars: Tell me again why Homosexuals want to be MARRIED??