Just had a convo on this topic at work, although I shouldn't have...at ended well though.
I think one important thing to keep in mind for Christians is why God is against same-sex relations. If the Christian claims it's because same-sex relations causes harm, then they will likely lose that argument. If they try to bring up all types of negatives, just to find negatives, then that will become apparent, and you might be labelled homophobic. As I brought up here and elsewhere, to say that same-sex relations are wrong and to not be a bigot or unreasonable, would depend on why you believe it is wrong, or not bringing up a reason that is clearly false.
I also think that the LGBT side should also be conscious of not labelling everything as bigotry and homophobia. When that label is misused or overused, then it can come off as an attempt to demonize and silence your opponent.