It depends. There are some libertarians who follow the homesteading principle dogmatically without really understanding why we might find such a rule to be useful in the first place. First, the primary principle that guides libertarian thought is the NAP, or the non-aggression principle. This also happens to be a variant of the golden rule but applied specifically to law. So, why might libertarians take the homesteading rule as an important rule?
It has to do with norms, conflicts, and the NAP. The NAP is “Do not aggress against another or his rightful property.” I think it may be easier to grasp some of the secondary but important principles in libertarianism, such as homesteading, when we look at the NAP/golden rule in the first person. In the positive form: “Respect me and what’s mine, and I’ll respect you and what’s yours.” In the negative form: “Don’t violate me or what’s mine, and I won’t violate you or what’s yours.”
So, I think once you read the NAP in the first person, the purpose of the homesteading principle (rule of first use) becomes clear. If I claim this water source as mine, you can either respect or violate that claim. So, the focus becomes about why someone might respect or violate the claim. The rule of first use is something that easily avoids conflicts and can help settle them if they do arise. Why not a rule of second use? How would that be more helpful than a rule of first use? It wouldn’t. The purpose of norms is to avoid and resolve conflicts. And few people would say, “Well, I built this house, and I would claim it as my own, but Joe over here has come along and claimed it as his under the rule of second use. So I must now give it up to Joe.”
No, people do not tend to do this. But what about the water source? Well, suppose you and I arrive on the island at the same time. We both see the only water source, and I sprint for it as fast as I can. I beat you there and I drink from it first. Then when you catch up and go to drink, I say, “No, you may not touch this. I used it first so it is mine.” Are you going to respect that claim? Probably not. You would probably be of the opinion that it should not be owned exclusively by only one of us. And you would be right. But the reason isn’t as arbitrary as it might seem. The purpose of any good norm is to resolve and avoid conflict. If a norm didn’t do this most of the time, it is a bad norm and would almost definitely be supplanted by a better norm. If I tried to “homestead” the water source, this would not resolve a conflict between the two of us. It is inappropriate to use it in that particular scenario.
So why homesteading at all? Well, because there is rarely only one of anything. People make a claim about something, and other people respect that claim. But for the people who don’t like to respect other’s claims, we have law. And I suggest you read What Law Is and A Praxeological Account of Law by forum member Clayton. So the rule of first use ends up being a rather good principle after all.
Also, just because someone might have a good reason to not respect someone else’s claim doesn’t make it right. But it is hard to make predictions from the armchair as to what is the proper course of action in many situations. Just because a man is dying of thirst doesn’t make it right for him to steal water from another person. But at the same time, it’s almost always absurd to think that the man dying of thirst ought to just die of thirst rather than steal the water. This is the importance of liability of actions. You are always liable for your actions. So maybe you are dying of thirst. And maybe you stole some water from someone in order to live. This does not absolve you of your crime. You have stolen, and the man you have stolen from has a right to sue you.
Anyway, I think I’ll leave it at that, because I’m pretty much just rambling now. I think the most important thing to take away from this is the NAP and why people choose to respect property rights, and that for when it breaks down we have law to help fix it.