I guess as long as they are regulated, monopolies can be beneficial to the society overall, in many ways intangibly. Bell Labs is a great example of something that kept on giving (Unix, C, etc).

I wonder what could make something like Comcast into a "good monopoly" though.

Another aspect is that commercial competition, while generally accepted as a system that in the end delivers superior results, seems woefully inefficient in terms of waste of resources, as opposed to something like academic competition, were people freely reuse competitors' previous work.