This is slippery-slope fearmongering. In reality, Apple has gone out of its way to ensure that Apple Silicon Macs can boot other operating systems if the user so desires, and can do so without sacrificing security.
Apple has publicly said that macOS is unacceptably insecure because users have the option of running unapproved software (https://www.theverge.com/2021/5/19/22444353/mac-malware-not-...). It's not unreasonable to think that they'd be interested in fixing that "problem".
Just give me a simple checkbox in the system settings that this is a "developer machine and I know what I'm doing" which disables all that stuff and it would be fine.
I assumed it would be much more frustrating than going back to Linux. Instead I've found fairly sensible documentation for solving nearly every issue I've run into, and a well stocked repo of applications.
Simply disabling it globally isn't really a good solution to the problem. Neither signed nor unsigned, notarized or un-notarized apps should ever be allowed to write to those folders, no matter if SIP is on or off.
OTH preventing an app to read/write subdirectories in the user's home folder is definitely not a useful feature.
They still haven't, haven't even made any big moves that way, but maybe eventually that crowd will be right in the same way that if you predict a recession every year, you'll eventually be right.