I have a couple of confessions. I'm Christian. I believe homosexuals should be allowed to marry.
BOOM!! In yo face! Seriously. I am not saying that I agree with the decision of homosexuality, but I am saying it isn't my business nor my place to put such restrictions on others.
However, it's far deeper than that. See, the problem shouldn't be centered on morality, it *should* be centered around WHY DO WE ALLOW THE GOVERNMENT TO DECIDE WHAT CONSTITUTES A MARRIAGE? Marriage is a God-given right, not a state-given right...at least it shouldn't be. All the "benefits" of marriage (on a material level) stem from things the government shouldn't be doing/involved in anyway! Income tax break? Thank you for allowing me to keep more of my money that you should never have taken in the first place. Health Insurance? Sweet, but the last time I checked insurance was something I bought as a "just in case" scenario, not as a method of paying for something I need, that's called a service, not insurance.
Marriage should not be decided and granted by our government, and the reason should be crystal clear: that power can easily be illfully used against me as well. If marriage is an issue of morality, then let the morality issue be about freedom and not your own preferences of what a marriage looks like.