I prefer the Austrian School, and the problem with a monopoly is that in the short term it's okay but in the long term it stagnates the industry by chasing out the competition. If there's no competition, then sure, things are fine now, but in the long run it wont' be so great and the quality of the service will decay and the prices will drift upward. They won't have a reason to care, so they won't care. Look at Comcast.
Another example you'll be very painfully aware of is oil. Why are gas prices low? Because OPEC (a thug group of oil-producing countries like Saudi Arabia and Venezuela) are flooding the market with cheap oil to try and put Russian oil and American fracking companies out of business. OPEC has the long-term income because of their oil reserves and because of how much money they have in the bank to take a massive blow of billions or trillions of dollars, and in return they completely destroy their competition who, like most normal companies, can't lose billions or trillions of dollars for any realistic period of time. Like a day. Or an hour. American fracking companies are still fledgeling and haven't been operating long enough to be in that position, and so far have had massive layoffs from the cheap gas. And then Russia is imploding, 'nuff said about that. If they put those out of business, they'll have the market cornered for another decade, and will make back an exponential amount of money they lost by slashing their prices right now. They did the exact same thing back in the 1980s, and it's how they came to be as powerful as they are now. What did they do when they had the monopoly? Controlled the prices. And it was okay at first. But it wasn't so okay for the past decade when oil was $4 a gallon, was it? It'll be even worse after this round of cheap gas if they get more market share from their plan.
So monopolies aren't good. They might not be bad for you right now at this exact moment, but they will be. Amazon, for example, is putting an extreme amount of pressure on the publishers they work with, and are costing them a lot of money. And it will hurt the publishing industry, and therefor the literature being published. They've outright cut the publishing companies off at the knees more than a few times when they tried to get control of their digital prices back.
In Austrian School economics, though, a monopoly isn't a naturally-existing entity. They only come about by government regulation because in a true free market the competition would prevent any one company from actually gaining that much power. Obvious examples are Standard Oil (Rockefeller), U.S. Steel (J.P. Morgan), and Western Union, where the government outright gave them the exclusive right to the business. And you know those names to this day. Less obvious examples of how government regulation of the market can create cancerous companies that feed off of the economic imbalance are Halliburton, Wal-Mart (primarily because of how it exploits a lack of workforce laws to drive cheap goods with third world labor), and Apple/Microsoft.
I listed both of those because they do the exact same thing via patent laws. The tech industry is bloodier than a gladiatorial arena right now.
Basically, a monopoly comes into being because America doesn't have a truly free market. We talk about it, but at the end of the day we're too pussy to actually do it. And so we have just enough regulation to cause ourselves marketplace problems, but not enough regulation to actually address the problems to protect the consumer or the health of the market. I'm not for market regulation, but if you're gonna do it then you have to do it right.