This comment deserves a much more detailed response than I'm able to give at the moment, but I can give some very brief thoughts:
Let me say that I have been working in AAA online game development for more than 7 years now;
I have worked on games that had 10's of millions of players, and these were full fat $60 AAA games.
Cheating was the second[0] biggest issue of our games, it sucked the entire enjoyment out- getting ganked by a bunch of players shooting through walls is not fun.
Why did we "allow" cheating?: Well, we never did, we used some of the best anti-cheat software we could afford, but it was still possible to cheat.
"Don't trust the client" is a common response, but being fully synchronised to the server has drawbacks too; servers typically "tick" at about 10-20fps, theres a lot of tricks we pull off to make it seem as if it's going the 144-240Hz of your monitor, like showing hitmarkers (but not damage numbers) to make it feel as if it's fast, if your movements were synced to the server you would feel as though you were walking through water, as the movement would be very slow as it needs to do a 150ms round trip to sync a step.
The truth of it is if we fully synchronised every action to the server: not only would it feel abhorrently slow; it would require a full 3d rendered simulation of the game world, we'd be able to run maybe 3-4 users on 40 core machines with 256G of ram... that's not feasible.
"Don't make online games" is another common response to hearing the realities and difficulties of making these kinds of games.
But I'd suggest, if that's your response; even if we made them that doesn't mean you have to install them.
We're both making a decision here: We decided to make an online game because it can be a lot of fun, you decided to install an online game because it can be a lot of fun.
Cheaters want to ruin that fun, we have woefully few tools to prevent that.
(by the by: I'm not in favour of kernel level anti-cheat, but fuck are cheaters the bane of my existence).
[0]: Biggest issue was actually bugs, but when we fixed bugs, cheaters were the next primary complaint.