When Rights are metaphysical, many others can be added by metaphysical arguements and they can be balanced between each other by utilitarian principles of the "greater good" and the like. He explains that this is why for the Unconstrained view holders (like the left) Rights held by the "many", like free speech", end up trumping a property right held by a lone individual.
"Rights" also suffer when held like an Ideology; as a magic formula that mere adherance to will solve all problems.
Sowell points out that Libertarians are a conflicted class and fall partly in with both views and have a problem therefrom.