"You didn't answer the most important question/argument: WHO decides whether that someone is racist/sexist, etc"

If somebody discriminates agains somebody else based on their sex or the colour of that person's skin then they are a sexist/racist. Nobody needs to "decide". That's literally what words mean. In the examples you gave, the manager would obviously be a racist.

Any "victims" who want to take action against an employer for discrimination *have to prove they've been discriminated against*!! The burden is on them, as it should be, to show there's a problem. If they can prove that there is racist or sexist discrimination in court (as has happened on numerous occasions), then what exactly is the problem?

If you think that anti-discrimination laws are equivalent to totalitarianism then I'm not going to waste any more time trying to convince you otherwise. There's obviously a reasonable middle ground that you're refusing to acknowledge, between "you must hire exactly 13% black people and 76% white people" and "it's completely fine if your company is 100% white males". And this was far more relevant during the racially segregated 60s than it is today.

Equality of opportunity means rule of law only when laws are fair to all people. That's what the civil rights act was for!!! To ensure that black people were equal under the law. But that meant that people who had refused to treat black people as equals were now "forced" to. I have no idea (and dwindling interest in) where your fear is coming from.