I tend to see rights as the precondition for a flourishing society. The straightforward arguments for self-ownership are Rothbard’s, and those Kinsella develops in How we come to own ourselves, not so much argumentation ethics. I think epistemological arguments like those Antoine de Jasay develops are the way to go, e.g. shifting the burden of proof on someone who would upset control over an object I homesteaded, as to why it is alright for them to do so. Keep in mind that for any society to exist there isn’t an “if” about property and controlling resources, only a “how” it’s to be done (collectivists tend to argue in a vacuum, as if the legitimacy of their own society’s claim to ownership is not in question or equally if not more specious than any other such claim.) He is going to have to come up with good arguments to show why he, as a third party, can merely go and take what someone else has acquired through their actions, and why he (or anyone more generally) has a better claim to it.