Here is “that guy.” You won't convince them with practical examples, because this is a matter of principle. Freedom and independence from the state are more important to these people than a few people suffering from lead poisoning. From their perspective, living a free life and then dying of lead poisoning is still better than being subjugated by the Leviathan.
> your second paragraph is at odds with your third
Well, well. That didn’t take long.
The teenager was a carefully chosen comparison. The state’s authority over the citizen is similar to a parent’s authority over their child. This is quite humiliating and emasculating. And I agree with libertarians on one point: if the state is against you, you don’t stand a chance. A healthy approach to this has two components. (1) You make sure that the authority is benevolent or at least allows enough leeway for a good life. (2) You create enclaves of freedom. The teenager hides his weed and smokes it secretly, or smokes his cigarettes on the way to school. The citizen leaves some income untaxed and runs a red light now and then. What does the teenager who categorically rejects parental authority do? Run away and become homeless? The difference between them and an adult is that the latter should have enough sense to realize that the romantic notion of a life free from the burden of authority ultimately leads to sadness, coldness, loneliness, and misery—or, if it succeeds at all, merely re-establishes structures in which forms of authority are entrenched. Libertarians feel most oppressed by the state every time they have to wait at a red light or obey a speed limit. They fail to see that, in doing so, they are submitting to a principle of order that is necessary for road traffic to function at all.
> Is that a semantic difference, or do you think there's something substantive to it?
That is a very important point! Philosophers distinguish between the particular and the universal. Libertarians recognize only the particular and reject any notion of the universal, because it negates all particularities. For them, a group is always just an accumulation of individuals. A genuine community—which consists precisely in the participating individuals restricting themselves to some extent for the sake of the community—is inconceivable to them as something positive. Hence the infamous Thatcher quote: “... and who is society? There is no such thing! There are individual men and women and there are families ...” That is an ideological divide that cannot be bridged through discussion. I’ve gone over this enough times already.