This is true, but I think that the specific point with respect to the usefulness of "rights" in determining what actions are permissible is still relevant. People's negative rights can easily come into conflict with each other. I'm also not convinced that "positive" and "negative" rights hold up well as a distinction. Is a right to clean water a positive right (some body has to take action to ensure that the water is provided) or a negative right (nobody is allowed to take actions which corrupt the supply)?