Excellent post, Larken. You know I've been following you for some years now, and I've challenged you with some of these "slippery slope" arguments in the comments now and again on Facebook. I think it's important for liberty-loving individuals to not become "mindless ideologues" and while not sacrificing principles, recognizing the analog world of "grey" means compromises have to made and reasoned, rational arguments for them have to be built.
If we're stuck in our ideology, we end up no better than those who have caused human suffering around the world but complain, "Well, my philosophy just wasn't implemented the right way. That's the problem!"
One challenge I have for myself and for the freedom community in general is this: Do we value freedom more than we value the wellbeing it brings? Some aspects of reality can be statistically demonstrated to lower wellbeing while restricting some freedoms increases it. I think it also introduces systemic risks which eventually, over time, lead to authoritarianism, so everything should be considered in terms of time-scale as well.
I really liked this post because, to me, it demonstrated your ability to remain principled while recognizing the challenges "the real world" faces. We have to pragmatic enough to recognize reality (such as the provably undeveloped nature of children's brains). The tricky part, I think, is recognizing that some adults also have under developed brains and some adults could be labeled "crazy" and shouldn't own a weapon designed to easily kill people. That said, if we're not careful, we'll end up giving authority to those who define who is crazy and who is sane.
I don't think "well-being" is the test that matters. Morality is. For example, I could improve some people's "well-being" by coercing them into eating healthier and exercising more, but I have no such right, even if it WOULD help them.
I'd argue your coercion would be more psychologically damaging than the health benefits. Morality only exists within conscious creatures capable of well-being (and pain/suffering). Morality is given meaning because of well-being, which is a very individual thing.
When @adamkokesh came through Nashville, we had a great time hanging out and he invited me to lunch and later dinner with his team. When I challenged him with this question, he gave a great answer in that well-being can't actually be a thing unless someone has the freedom to decide what it is. Some people, as an example, are into S&M and for them being whipped increases their well-being. For others, the same activity is horrific. Voluntary consent is key because they are making free choices about their own well-being.