You might wanna read this: It’s Michael Bauwens - the president of the Belgian based Murray Rothbard Institute (where I’m a member from) - defense of natural law/natural rights and it’s basically a longer version of what I’m writing here. (I get my ideas from him.) (Link: http://www.independent.org/students/essay/essay.asp?id=2342)
Anyway, to answer your questions.
“He was the first to give the thing a meaning, so it is his. Not sure about that. Why does giving meaning to something make it yours?”
<= What does it mean to say ‘it is his?’ It means he can control it, right? Well: first of all: he was the first to take control over it. At that time, there was no one conflating use - because he was, in fact, the first one. If someone challenges his control, they have to come after him in time. And to challenge control, means to claim that you’re decision to control it is superior than his. But based on what grounds? If nobody challenges the meaning you are giving it, it means that nobody cares. There is no problem of ‘law’ at that point (imagine Robinson Crusoë on an island: he also doesn’t have the problem of what he should do, because there is no one else.) But when someone challenges the control, he’s claiming control of itself. But since he’s attacking the (prior) reasons of the other guy, he’s attacking the other guy as a praxeologogical unity. The praxeological body is a whole: there is no difference between me ‘using’ my body and me ‘using’ my property.
Edit: Because it was a ‘thing’ - a res nulius - and now it’s a means it has to belong to ‘someone’. Maybe not lawfully, but praxeologically: he was the one that first controls it. He turned a ‘thing’ into a means.
“Using the means created by another actor is aggressing against his conception of the world. Do we have a right, derived from self-ownership, to not have our conception of the world aggressed against?”
<= Well, it’s based on the previous notion. Law is the concept that differentiates between actors in a scare world. You is use and me is me. I control me and you control you. Aggressing against another actor is aggressing against a moral equal, who also gives meaning to the world. The connection is that because you give reasons, you have a moral obligation to act reasonable in the face of others. This is because the position ‘I don’t have to be reasonable’ cannot be defended. If it cannot be defended (by logic) it’s simply nonsense. There is a moral imperative in the notion ‘one ought to act reasonable’.
A conflict between actors - 'I want to use this means of you - would be acting unreasonable, because you wouldn’t able to defend why your reasons were better than the other persons reasons and should be overriding his conception of the world. (If you can, than the other person is just agreeing with you and there is no aggression (anymore).)
“As for the praxeological body, defined as “the actor and it’s means,” being a unity… I’m still lost. Unless I’m misreading or misinterpreting (highly likely), it seems like you are just stating this relationship is true, without saying why it is true.”
<= The praxeological unity isn’t a ‘moral’ category. There is no ‘we ought to be a praxeological unity’. It’s a natural concept: we are a praxeological unity. If we understand the concept of ‘action’ - employing means in the world - than you have the concept of a praxeological unity. We act and the means we use - our body and things (that become means) in the outer world - have a logical identity. They don’t look alike, but they have the same status in our action: they are means and we control them.