Why should the government stop people from hurting themselves?
The usual answers fall into three categories. There is the “no man is an island” rationale, the “we don’t want to have to look at you” rationale, and the “they’ll go on a rampage and destroy civilization” rationale.
Under “no man is an island” we find the observation that lots of people, even in a non-welfare state, have people depending on them. Interdependence is an inescapable feature of specialization, which is itself the only known method of producing for ourselves anything better than a cave-man existence. And even the majority of cave-men operated as tribes rather than solitary nomads and hermits.
Of course the mere fact that we live by trade doesn’t mean that other people are inescapably or unfairly harmed by your destroying your productive capability or by your simply leaving the area alone. What makes the difference is whether or not you have gotten some benefit by promising extended cooperation – if you have, and you deliberately destroy your ability to make good on that promise, then you have thereby unjustifiably harmed your trading partners. Of course, again, you do the same thing if you simply leave the area (i.e., “skip town”). But somehow, that doesn’t seem to justify either heavy criminal penalties for skipping town or massive regulation or prohibitions on selling other people the means to skip town.
And this rationale also fails to take into account that no one is (or should be)forced to make any deals with you that require extended cooperation on your part, and that no system can even theoretically supply perfect enforcement of contracts. While past performance is no guarantee of future results, a socially liberal regime without any welfare or forced trading would tend to encourage people to avoid relying on promises from people most prone to breaking them (such as known drug users) and also encourage people to keep promises and avoid things (such as drugs) that would prevent them from doing that. And really, if unreliable people are willing to give you extra clues to their unreliability (such as the physical changes associated with drug abuse and the presence of recreational drugs in their bloodstream with no medical rationale), why in the world would you want the police to stop them?
The second category, the “we don’t want to have to look at you” rationale, relies on the theory that the very existence of visibly impoverished or damaged people causes the rest of us harm that we have the right to be protected from by force of law. This harm can be aesthetic, or it can be unwanted pity. Either way, it ends up becoming a legal obligation to remain wealthy and healthy enough to spare other people’s feelings, or to make other people wealthy and healthy enough (out of our own pockets) to spare the feelings of still other people. This insanity gets extended to the point where the cost of bailing you out after you did something dumb is counted as an expense that you caused them, and even as an expense that the people who sold you the means to hurt yourself caused them, as if getting bailed out were a law of nature and your benefactors had no choice in the matter. (It may be a law of Congress, and your benefactors may indeed have had little choice, but the cost was imposed by voters and Congressmen, not so much by you and certainly not by your trading partners). You may not like seeing people that have spent or loafed their way into poverty, especially if they’re old, or people that have wrecked their bodies by neglecting safety precautions or abusing drugs, but that doesn’t mean that you have the right not to ever see such things or to banish them from existence, or to forbid grown people from taking a risk that such things will happen to them. A “decent country” is not one in which poverty or injury never happen; it’s one where people are allowed to take risks (and bear the losses – if they didn’t, it wouldn’t really be a risk, would it?) in their pursuit of happiness.
Deriving moral laws and everyone’s unchosen legal obligations from people’s emotions makes about as much sense as deriving the laws of astrophysics from people’s emotions. If humans are born with any sort of moral instinct, it would necessarily be more appropriate to hunter-gatherers than to technologically advancing civilized people that aim to stay that way.
And finally, we come to the “they’ll go on a rampage” rationale, usually with the unstated premise that the people who aren’t given unearned wealth and try to take it by force are the good guys, and their targets (especially if they defend their property with force) are the bad guys. A more perfect misunderstanding of the moral issues involved is difficult to imagine, but if that dark day comes to pass, it will make no more sense to blame ourselves for driving the oppressed laborers to terrorism than it does now to blame ourselves for driving oppressed Muslims to terrorism. Paying them ransoms in either case tends to escalate their demands rather than appease them. I say “millions for defense, not one penny for tribute”, whether it relates to Muslim radicals or homegrown would-be socialist revolutionaries.
Be careful not to drink the kool-aide that the depressed, despondent fellow made.
There is another arguement you leave out. There is certainly a level of addiction within a society that will threaten its existence. At a societal level, the individual is an investment of resources (childhood), and someone who goes off the deep end (or even just commits suicide at 16), is obviously a dead loss at that level – even if no one forces anyone to expend additional resources keeping them alive once they become adults. This is obviously more critical in a poor society, where the survival margin may be quite thin. (Many of the social taboos that are generally lumped under the label conservative are critical to survival for marginal societies) The American economy obviously has a very large capacity to carry dead weight – but even it is not infinite.
Obviously you can still have social taboos without them being enforced by the government. Still, in a democratic society, it can be reasonably argued that there is a degree of overlap, and that the lack of a statutory prohibition undercuts the social stigma.