It has been stated before in the thread, but it bears repeating. For far too long we have allowed the opposing viewpoint to dictate the terms of the debate. We have allowed ourselves to be pushed into the position of arguing with someone who has never really constructed a lucid argument in the frist place!
The liberal assumes a priori that gay marriages are good and should be a right that should not be interfered with and then asks the conservative, "Why not?"
Unfortunately, the liberal has not yet ESTABLISHED his/her argument. Stating a belief and establishing an argument are not the same thing.
A tactic that is very helpful is to get the liberal talking. (I offer you Exhibit A: John Kerry's gaffe before the election.) Liberals have very poor thought processes, not because they are intellectually inferior. No matter that they frequently look like intellectual inferiors, their main problem is they engage only the heart and do not temper the heart with the mind. The Bible says that the heart is desperately wicked and no one can know it. So, it is easy to understand how someone ruled by their heart can come to embrace all kinds of desperately wicked things!
Above all, if you hope hope to pursuade any of them that your Christianity is of value, do not be goaded by their disdain for all you hold dear. They will spit on it as they spat on Christ. Nevertheless, out of concern for them, at all times remain respectful. That is why i ask thousands of questions about what they think and catch them with their own inconsistencies...which, never fear, WILL come up.
Sorry, I have n magic bullet for you, but I heard of this technique first from Francis Schaeffer....you must read his book "Escape From Reason"!!!
*whispers to self,"spell check is my friend"*