We're talking about areas where there has been no competition, and the incumbent has already succumbed to the same exact lethargic rent-seeking that people ascribe to municipal services.
Also it appears you seem to be thinking that "municipal fiber" means there are employees at City Hall with a blank check from the general fund. WG&E is a separate corporate body, overseen by the City of Westfield. I would guess they will be doing operations for Charlemont et al, but Charlemont will be free to choose a different operating contractor in the future.
So what we're really talking about is the ownership of the built-out infrastructure, which government has traditionally been paying for anyway - this story is about Charlemont not giving $500k to Comcast! The idea that the government should pay to build out infrastructure to be owned by a private company isn't the "free market" - it's textbook corruption!
For context - I am libertarian, and I recognize that there is no difference between government and a de facto monopoly that one is forced to patronize. In fact, the latter is a great way of describing the former. If you want to make a philosophical argument that government has no business subsidizing communications infrastructure at all, I won't argue. But that is generally not the point of contention around "municipal broadband".
Do you not see any difference between vigorous competition among profit-seeking companies, where mis-steps can cause loss of profits, loss of jobs, and ultimately bankruptcy and competition between a company with risk on the line versus a municipality that doesn't have to take on any of those same risks?