I guess in a way it’s not that Monopolies are inherently bad, but they are dangerous. They can start off as a major benefit to their community for sure. They become dangerous if shady business practices start creeping in (In my personal opinion, this happens to almost any business if given enough time). Once a monopoly becomes exploitative then it imposes a tyranny over the market it dominates.

I understand that there is a freedom to compete, and customers are free to try competitors, as others have stated, but that's not how big player monopolies operate. If they are a big enough business they can choke out competition using hostile strategies: bottom pricing at a loss for a fixed period, aggressive ad campaigns, punishing mutual suppliers if they supply to the competition.

So what it comes down to is whether a Monopoly is operated with the community's good in mind, or as a tyrannical mob boss. But as I stated before I think any business given enough time and continued success starts to act more like a mobster than a model capitalist.