I'm sorry, but if you truly believe that sexual orientation is something you're "born with", then failure to support same sex marriage is hateful and discriminatory. The whole "born with" argument is designed to make it a discriminatory offense. Rubio's "positions" on this either mean he's pandering to the gay vote, or he's in favor of discrimination for the "right reasons".
Personally, I have no issue being against same sex marriage because I do NOT believe you're "born that way", and I believe that SSM is a perversion of the Biblical intent of marriage.