Shens. Learning not to be a dick is part of growing up, and sometimes that involves getting shot after being a dick. It's better to shoot them before they have a family that relies on them.
But then who would stop bullying? We've seen that parents and schools are useless when it comes to bullying. Guns are effective almost every time.
Not that I'd exactly agree that every bullying situation is best resolved with weapons, but there is a very good point to that.
We learn, not only from our personal mistakes, but also those of our peers. That's how communal rearing and education actually works, in terms of preparing for life (as noted: school is about far more than pure book-based education) and setting them up for success.
But social Darwinism has always been present in our history as a species - if you see Bob over there continually harass Ed, and then one day witness Ed slaughter Bob, you may or may not learn that harassing someone in that way might not be a good idea.
Of course, how schools handle these things, how they impart the lessons of social interaction, has degraded terribly, and a lot of people really aren't learning the fundamentals behind all of this. It's not "don't be a dick to people because that's wrong", it's become "don't be a dick to people you think are unstable, because they might kill you." As such, these people are still likely to escape formative years healthy and intact, and go on to contribute negatively society in various ways.
But ultimately, if we as a society actually returned to such old times where punishment was far more brutal, to a degree (not stone-throwing or torture-rack style, but public humiliation and more executions [humane, of course]), then so many unfit adults wouldn't proceed to live long enough to have a family and contribute in any way toward society. Sure, you may lose some great thinkers who had made one or two terrible mistakes... but you shed plenty of the unfits who would only degrade society in the long run (oh, hey... about that), and thus, give a far better chance for the more fit leaders to actually produce a positive impact on the world around them.