Well, they’re often economical for the patent holder in the short-run. But over time, a legal regime that discourages information-sharing simply closes off advances in technology. Defenders of government-granted monopolies (i.e. patents) often rely make broad claims that allegedly show that inventions would not be made were it not for patents. True history, on the other hand, generally shows the exact opposite as in the case of William Gilmour and the power loom. James Bessen writes:
Although Gilmour and Lyman directly helped competing mechanics and textile mills, they weren’t fools. For two decades, machine shops and textile mills made high profits. Machine shops could charge high prices for textile equipment because few mechanics knew how to build them; textile mills could make high profits because it was much cheaper to use the new loom. Imitation didn’t substantially reduce profits because there was a shortage of mechanics who could build the machines, of entrepreneurs who could run the new type of enterprises, and of skilled workers who could make the new contraptions productive.