I strongly suspect that what you'd find is that Comcast would simply "pass" on trying to compete in those towns. Comcast loves towns where they can be a monopoly provider (like mine) and in a case where there'd be bloody competition against a municipal provider, I suspect they'd rather fight on another front.

How badly do you want to be a taxpayer in a city with a government that’s determined to spend out of the bottomless public purse to compete with Comcast?

It's the other way around, actually. Private ISPs cannot survive without statutes that prevent the establishment of municipal ISPs. Like all utilities, Internet traffic has a very low per-unit cost, making it unviable to turn a meaningful profit without engaging in predatory business practices.