There exists certain sectors of the market that, by their very nature, end up becoming monopolies, and, therefore, anti-competitive. The most obvious example of this would be utilities (think power distribution (even the poles themselves), water mains, sewage, etc). Is there any way to combat these sorts of monopolies with the existing system, or would a new system have to be devised using decentralized alternatives?
Monopolies are the opposite of free markets. Even pseudo-monopolies are counter to free markets as they inevitably use their dominance to manipulate the markets in their favor.
That said, I feel like there are a lot of libertarians who feel like free markets are core to the philosophy, and about as many who believe that free markets are a nice-to-have, secondary to everyone doing whatever they want in the market regardless of its impacts.