Imagine that one person, or a small group, wants to do something, like watch pornography, do uncertified medical procedures, have gay sex, worship Satan, shoot guns, drink raw milk, etc. Imagine further that many other people outside that small group don’t want them to do this. They instead want the government to make a law prohibiting similar groups from doing similar things.
In this prototypical situation, libertarians tend to say “let them do it” while others say “have the government make them stop.” If we take a cost-benefit perspective here, then the key question here is whether this small group gains more from their activity (or an added increment of it) than others lose (including losing via their “altruistic” concern for the small group). Since this small group would choose to do it if allowed, we can presume they expect to gain something. And if others complain and try to make them stop (or cut back), we can presume they expect to lose. So we are trying to estimate the relative magnitude of these two effects.
I see three considerations that, all else equal, lean this choice in the libertarian direction.
Law & Government Are Costly – It will take real resources to create and enforce a law to ban this activity. We’ll have to negotiate the wording of this law, and then tell people about it. People will complain about violations, and then we’ll have to adjudicate those complaints, and punish violators. We’ll make mistakes in which laws to create, who to punish, and how to manage the whole process. More rules will discourage innovation, and invite more lobbying. All of which is costly.
Local Coordination Might Work – If people do something that hurts those around them more, often those nearby others can coordinate to discourage them via contract and freedom of association. If playing your music loud bothers folks in the apartment next door, your common landlord can set rules to limit your music volume. And kick you out if you don’t follow his rules. The more ways that smaller organizations could plausibly solve a problem, the less likely we need central government to get involved.
Lawsuits Might Work – Legal systems have well-established processes whereby some people can sue others, claiming that the actions of those others have hurt them. Suit losers must pay, discouraging the activity. Yes, people harmed can need to coordinate to sue together, and yes legal systems tend to demand relatively concrete evidence of real harm, and that the accused caused that harm. It might be hard to figure out who to accuse, the accused might not have enough money to pay, and the legal process might be too expensive to make it worth bothering. But again, the more situations where the law could plausibly solve the problem, the less likely that we need extra government involvement.
Again, each of these considerations leans the conclusion in a libertarian direction, all else equal. Yes, they can collectively be overcome by strong enough other considerations that lean the other way. For example, I’ll grant that for the case of air pollution, we plausibly have strong enough evidence of large harms on outsiders, harms insufficiently discouraged by local coordination and lawsuits. So yes in this case central government might be an attractive solution, if it can act cheaply and efficiently enough.
But the main point here is that the three considerations above justify a libertarian default that must be overcome by specific arguments to the contrary. If outsiders complain about an activity, but aren’t willing to buy less of it via contract, or to sue for less of it in court, maybe they aren’t really being hurt that much. There is an asymmetry here: if we don’t ban an activity and might get too much, contract & law could reduce it a lot, but if we ban an activity and might get too little, contract & law can’t increase it much.
Yes, other persuasive contrary considerations might be found, including considerations not based on the net harm of the disputed actions. But the less you think you know about these other considerations, the more your choice will be influenced by these three basic considerations, all of which seem to me pretty solid.
While I have said before that I am not a libertarian according to common strict definitions, I still usually tend to lean libertarian, because in fact arguments based on further considerations often seem to me pretty weak. While one can often make clever arguments, it is often hard to have much confidence in them; the world seems just too complex. And so I often have to fall back on simple defaults. Which, as I’ve argued above, are libertarian.