I could understand the reluctance to approve of same sex marriage and other rights of the gay community if being homosexual was actually a choice.
If it was a choice and a person wanted to get married, you would think they would only date people to whom they could actually be married one day, i.e. opposite sex people. Most marriage minded heterosexual people make this choice by dating people available for marriage and not dating people not open to or compatible with marriage; for example already married people or those who don't agree with their religion, etc., etc., etc.
However, how can someone actually believe it is a choice in the first place?