Believe what you want to believe, whether it is in faith or religion, but there is a difference between honouring your way of life, and contributing to the oppression of others, especially those who may not share your values. It’s fair to say, that if we make personal decisions regarding what belief systems we choose to follow and practice, we should allow others to do the same. No belief system should be awarded higher standing than the other. The equality in basic human rights should always remain the same.
You may not believe in same sex marriage, that is your right, you are lucky enough to sit on the privileged side of this debate, but to oppress others is not progressive and extremely harmful.
Simply put, if you don’t want to marry someone of the same sex, then don’t.