The difference between historical feudalism I think arises from the rejection of the idea of slavery, or anything like it.
Though one could probably argue that if you're unable to sell yourself to a lord it infringes upon your ownership of yourself.
Being able to walk away from the arrangement does seem like a crucial component of anything that would allow it to be called libertarian or voluntarist. At the VERY least in the event that the lord, as it were, were to be in breach of the original terms of the contract.
At the end of the day though the ideas of free markets, voluntarism, libertarianism, etc, is that coercion is less productive than free exchange, given a broad enough scope. And that in resorting to coercion rather than free exchange a would be statist undermines their own wealth.
But yes, in practice, the ability to externalize the costs while internalizing the profits does come up time and again as a very stubborn reality we get to contend with.
