Technology

Since they shut out Linux players last week. Taking away access to things someone bought, used and can't use anymore because of something the supplier did could be interpreted as theft.

Nobody likes cheating.

However, a lot of people don't like anti-cheat mechanisms that are essentially rootkits, and especially nobody likes when a product is changed long after it's release in a way that makes it unusable (as the new anti-cheat forbids Linux).

No one decided cheating in multiplayer games is fine. But invasive anti-cheat software is significantly worse, and frankly doesn't actually work. Automated detection tools can help, but ultimately you need mods / admins to properly stay on top of cheating. Trying to replace those jobs with incredibly invasive software installed on every user's device is just a sign of a trash developer or publisher.

If you play in Linux assuming this game even runs on Linux. Good chance they will ban you from running this game on that OS. They could allow it but most companies see Linux as a minority and will mostly willing to take the hit of blanket banning the whole OS. I guess Steamdecks would be out of question now. Another is security risk this kind of anti cheat tend to be invasive they have access to your kernel, the part of the OS that has access to everything on your system. If that thing is compromised good chance you'll be affected also if you that in your system. Think of something like clowdstrike issue.

Aside from it being code you don’t want on your machine

Code you don't want on your machine, that have sometimes more permissions than you yourself have on your own files, is completely opaque, and have the legitimacy to keep constant outgoing network data that you can't audit.

Yes, aside for that, no reason at all. No problem with a huge risk on your privacy for moderate results that don't particularly benefit you in the long run.

(and all that is assuming that they're not nefarious to begin with, which is almost impossible to prove)