That seems like a very circular answer. I'd clarify to say that patents
are considered anticompetitive practices. However, they were (as originally envisioned, but certainly not since State Street, possibly earlier) anticompetitive practices that were specifically and purposefully limited in two ways:
1. The filing of a patent requires the filer to disclose the operation of the patented invention such that any art-practiced person could replicate it. Any non-disclosed secrets are protected only under trade-secret law, where the thing is secret only until the secret is out. That's how Coca-Cola has kept the Coke recipe a secret for generations.
2. The patent is enforceable only for a limited period of time (20 years), much like copyright originally was (14x2). Due to innovation pressures, and the fact that companies recognize they build on one anothers' works, that enforcement window hasn't been extended. Instead, companies rely on patent thickets to keep competitors out for the proscribed period of time.
As mentioned above, modern patents aren't actually subject to these limitations. Modern drafting lawyers do everything they can to exclude required information in the patient itself so that it can't be used for reproduction, while still claiming patent enforceability on the result. Additionally, patents are also awarded for a vast array of inventions that would've been previously considered unpatentable descriptions of ideas (software and process patents in particular). See Jefferson (e.g., knowledge and candles) for some of the original reasoning behind the system.
In other words, since there's no billion dollar industry buying laws requiring fewer and smaller patents, the scope of patentability keeps increasing to the benefit of already entrenched players.