> Being a monopoly isn’t illegal. You have to also behave anti-competitively.

Which is why it's reasonable to some that someone getting in trouble for "being a monopoly" is actually getting in trouble for some specific actions they took.

right, hence the "specific steps taken", and actually when in the history of the world has a monopoly existed that has not taken anti-competitive actions?

People having monopolies have a strong urge to maintain them, the means to do so, and not doing so might actually require lots of thinking and trying to walk a very thin, straight line.

on edit: ok it seems this post mentions a monopoly that takes no anti-competitive steps, which is a company I've never heard of https://news.ycombinator.com/item?id=41642040 but if they have 100% of the market I guess there's no reason for them to be anti-competitive, that kind of thing comes when you have 80% of the market but it's threatened (guesstimate)

If you are not anti-competitive you won't be a monopoly.

"I didn't get rich by writing a lot of checks" -- Bill Gates

That's a quote from the character Bill Gates in the Simpsons, not actually Bill Gates. A true quote from Bill would likely be much worse.

Sure you do. ASML has a famous 100% monopoly on advanced photolithography machines, but I've never heard anyone accuse them of anticompetitive behavior - there's just nobody else who knows how to make them so well. I guess it's not how Visa works though.