They're not particularly strong arguments unless you are already convinced of the conclusions. "Natural law" (constraints) can be demonstrated to be necessary f

They're not particularly strong arguments unless you are already convinced of the conclusions. "Natural law" (constraints) can be demonstrated to be necessary for societal functioning, but they don't extend to "natural rights". That is, a societal necessity to prohibit unsanctioned killing of its members does not in any way imply a right to life. And the idea that the natural state of humanity is the lone savage is entirely unfounded (and contrary to all evidence dating back as far as we can manage it); it's merely a convenient way to begin an argument that ends up "proving" its own unfounded premises.