It depends, some people distinguish economic rent from economic profit by restricting it to economic profits that cannot be reduced to normal by competition in the long run. Some additionally include profits without any opportunity costs.

Economic rents run counter to properly functioning markets, e.g. by raising artificial barriers such as patents or counterproductive regulation.

The key tenet of perfect competition is that in the long run, only normal profits exist. Since economic rent stands contrary to this, it cannot be a fundamental law of capitalism. In fact, economic rent is a sign of market failure. But this is reality and markets can't be perfect, so we try for good tax policies to redress this imbalance. Look at the section on rents here: http://www.economist.com/economics-a-to-z/r#node-21529784

As an aside, people think Thiel's idea on monopoly is controversial, but really it's just a catchy way of portraying the observation that, since in well functioning markets, competition leads to zero economic profit, you should always be seeking advantages (innovating) and situations which allow you to (temporarily) extract economic profit.