Since Microsoft has access to your entire windows system, there's no harm letting every other company have it too then?

No, it doesn't, and you're betraying your ignorance of the topic by making the suggestion.

First of all, when we refer to rootkits, we're talking about the fact that NProtect, by design, gains an absolutely staggering amount of access to the kernel space of your computer. VAC, by comparison, does not demand anything like the same level of access. You're making an apples to oranges comparison, and when questioned on it responding with "But they're both citrus fruit, right?"

No, they're not, and the fact that you think they are means you don't know nearly as much about this subject as you think.

But putting that aside for a moment, suppose one day you went hang gliding. Then, upon telling me about how much you enjoyed it, I immediately demanded that you play Russian roulette with me, and got seriously offended when you refused. That would be insane, right?

So you see how a person consenting to one risk doesn't obligate them to consent to others? It's not an all or nothing state between "My computer is exposed to exactly zero vulnerabilities" and "My computer is exposed to literally every vulnerability ever".

Every single program you install on your computer brings some potential amount of risk, but a) that risk is MUCH higher when the program demands the kind of kernel level access to resources like your memory that NProtect wants, and b) that risk has to be commensurate to the benefits offered, and it's hard to see what benefit I'm being offered by a notably cheaply made kernel level anti-cheat in a purely cooperative gameplay experience.