I think 'pro-gun' is a bit different.... in fact, I think a better analogy would be people who want citizens to have the right to use a gun in self-defense against an intruder. You wouldn't say the person who is in favor of legal self-defense is 'pro-shooting-people', they just want people to have the right to do it if they need to. Someone who is 'pro-choice' doesn't want everyone to go out and have abortions every day, they want a woman to have the right to one if they need it.