What's your evidence for that?

The history of fair competition comes to mind. That's needed for things to work.

Competition breaking and being unfair goes back to at least ancient Roman law, here's a Wikipedia article on it: https://en.m.wikipedia.org/wiki/History_of_competition_law

If the 2,000 years of examples there isn't enough I can provide lots more.

The competition zealots only have "thought experiments" and pretend like there is no history to this stuff.

I'm not sure what you mean by only thought experiments. There's lots of history of cartels falling apart, monopolies being broken; or very often also: monopolies being upheld by the government, and sometimes supposed anti-trust law being used to keep out the competition.

Lots of the laws mentioned in the Wikipedia article you linked to are pretty anticompetitive. Eg

> Under Diocletian, in 301 AD an Edict on maximum prices established a death penalty for anyone violating a tariff system, for example by buying up, concealing or contriving the scarcity of everyday goods.

Or just next:

> It provided for property confiscation and banishment for any trade combinations or joint action of monopolies private or granted by the Emperor. Zeno rescinded all previously granted exclusive rights.[4] Justinian I also introduced legislation not long after to pay officials to manage state monopolies.

It's all about government enforced monopolies.

On the more positive side: have a look at eg Herbert Dow and the breaking of the German Bromine Cartel. (Eg via https://fee.org/articles/herbert-dow-and-predatory-pricing/ or look at any other article you can find on that.)

Or George Selgin's Good Money (https://www.goodreads.com/book/show/3392302-good-money) about an episode in the English Industrial Revolution when the private sector minted coins because the government monopoly was inept.