If you get monopolies, they are considered bad only when they become an obstruction to improvement and inventiveness, because if the prices ever rose enough to justify competition again someone could enter the market, assuming it was a market like on-line retail where you can't crowd out competitors from store shelves.

Internet is a terrible commodity, because so much of the cost of connectivity is wrapped up in laying lines and buying server farms than actually maintaining the infrastructure. And that is really what it is - there is a reason roads aren't private, and why no other animal ever evolved wheels. Some things are best done collectively, and I usually lean libertarian but infrastructure is something you can't effectively leave open to free markets or give to private monopolies, because they are so easy to take through monopolistic practices.

It's a question of barriers to entry. Restaurants have not formed a monopoly in any country in the last 1,000+ years. However, places like Disneyland or the Pentagon will often prevent open markets and create a small internal Monopoly on food.

As to cable and high speed internet / cable. Most locations prohibit completion, artificially limiting which company's can sell cable in a given area. They had a rather tough fight getting off the ground even for an incumbent like Verizon.