I doubt the goal is to "stop any homophobes from watching the movie". The goal is to (1) Honor the commitment to diversity that Trek is known for, (2) Acknowledge and show respect for gay fans and the gay community in general, and (3) Encourage tolerance in a new generation of Trek fans by establishing that one of their heroes just so happens to be gay.
Of course they want the homophobes watching the movie. That is why they went with the safest choice possible for introducing a gay character and likely just give him a little scene or two. And point 1-3 would have been even better achieved with a more prominent character. Ideally they should have already made in ST09 one of the bigger main characters bi or gay.