If our best shot (pardon the pun) is to prevent crime by making people scared to commit it then our society is pretty screwed long term anyway. The deterrent that prevents me from breaking into peoples houses is the conflict with my principles - the basic feeling that it is wrong.

Unfortunately not everyone shares the same moral principles. In fact, apart from religion (and not all people are religious) there is no compelling reason to follow any moral standard at all. I also can say that Martin did not go to jail peacefully because his moral principles told him to; he did it because he’d end up getting shot if he didn’t obey. Making people scared is the only way to prevent crime unless either all people adopt the same religious code (not likely until the return of Christ ) or someone comes up with a pragmatic reason for all people to adhere to the same moral standard. And saying “for the benefit of society” doesn’t work, because no one really cares about society when it comes down to a personal gain or loss.