Tell that to anyone who ever mugged someone else, burned down a house then shot the survivors as they came out, or ran a concentration camp. Apparently your "rational self-interest" was no deterence there.
But if I disagree -- where then is your right? It only exists then upon being enforced.
Nope, it exists because we [rationally] do not want to be assaulted. So we selfishly agree not to assault each other, or others, and codify that agreement into our law. Thus our selfish individual non-assault right exists whether or not it is violated/enforced.
And if we do not agree? That is rather the point. You are assuming (rather academically I might add) that everyone, or even most people, are of course "rational". I suggest that your perspective has been shaped by your environment. Go live in Liberia for 6 months in the bush and then come back and tell us about it. Try discussing your "enlightened rational self-interest" to someone who thinks chopping off your arms with a machete is fun and besides, he wants a snack. Have fun trying to discuss your concept of "inalienable" rights (sans God or social group) while they turn your forearms into "meat on the stick".