In my third link in a row to something on LewRockwell.com, Michael S. Rozeff defends the concept of "natural rights".
The main problem, in my view, to any theory of rights that does not recognize some objective basis for rights (i.e., some form of natural rights) is that ultimately, such a system makes the concept of rights a mere custom, without any real moral import. In otehr words, without some concept of an objective morality, without some from of "natural rights," rights become a mere preference. Violations of rights then become merely a deviation from culture, rather than a terrible offense.
It seems to me that those who deny the existence of natural rights usually do so because they wish to substitute a system of rights based on their preferences; that is to say, what is right and wrong in a given situation depends on whether or not they like it rather than on particular axioms of right and wrong.
That is all.