Mucking about in the kernel basically bypasses the entire security and stability model of the OS. And this is not theoretical, people have been rooted through buggy anticheats software, where the game sent malicious calls to the kernel, and hijacked to anti cheat to gain root access.
Even in a more benign case, people often get 'gremlins', weird failures and BSOD due to some kernel apis being intercepted and overridden incorrectly.
The solution here is to establish root of trust from boot, and use the OSes sandboxing features (like Job Objects on NT and other stuff). Providing a secure execution environment is the OS developers' job.
Every sane approach to security relies on keeping the bad guys out, not mitigating the damage they can do once they're in.