Except that so many industries these days have such a massive barrier to entry that it's not hard to envision a scenario where there is no competition. I can't even believe you're sitting here defending monopolies. Do you have a literal shrine to capitalism in your bedroom? Because it honestly sounds like you do worship the concept.
Well, I'm sure it's not a patch on your Lenin shrine.
Look, I have explained the role of each of the factors in libertarian theory over and over and fucking
over. Frankly, I'm getting tired of it. I'm starting to see why Ascent just says 'here, read this book' every time we corner him on something. It's fucking tedious.
Let me see if I can tl;dr it down to something you will actually read.
Companies (not 'Corporations', those are the bastard children of Government) provide for-profit services. This would include much of what Government now claims to do, that being protection and justice.
Charities pick up the slack on things that can not be provided for profit, such as homeless shelters, and the like. What government calls 'social programs' This would also include pure research projects, such as deep-space probes.
The Media keeps these two honest by investigating and reporting on them. If you're worried about bias, seek the opposite bias (you can count on Pepsi News to report on Coke's misdeeds, for example), or seek an unbiased, donation-based show.
All of these are kept in check by one simple fact: competition. There is a limit to the amount which the barriers to entry can be raised. Competition is not, As I demonstrated earlier, limited to only that specific field. If you price your service too high, people will not use it, and seek another service, or the profits will exceed the barrier to entry costs - a purely subjective calculation, you can never know exactly when a competitor will pop up.