The conceptual problem with patents is that they grant an artificial monopoly on something, just like copyright does. That's a distortion of the free market, so

The conceptual problem with patents is that they grant an artificial monopoly on something, just like copyright does. That's a distortion of the free market, so if you believe in free markets, a priori they shouldn't be allowed. To argue otherwise, you will need to show that a practical system can be created that will do enough good to outweigh the artificial monopolies created.