The ability to regulate monopolies (or corporations in general) for the preservation of public good is written into the constitution (the Commerce Clause specifically). If you are actually trying to defend the right for people to form trusts/monopolies that serve no greater purpose than maximally boning the public to almost no one's benefit, you're a loving handicap.
Supply and demand. Supply bad ISP. People demand better ISP. Another company offers a better ISP and therefore prospers. It's like the core principle of capitalism.
Literally 100% bullstuff. What you wrote is a completely bullstuff falsity that we literally disproved in my introductory economics class in college.
Monopolies
do not have supply curves. They are price-setters, not price-takers. What this means is they'll always charge their profit-maximizing price at the cost of all consumer surplus. This, regardless of which school of economics you subscribe to, is a
bad thing.
Another company can't offer a better ISP if nobody is willing to fork over literally billions of dollars in capital to set up the cable and infrastructure to run one.