Hate isn't "science/math/etc". There isn't an algorithm that can objectively look at speech/data and say it is hate without causing a lot of issues of friendly fire.
If jew says I hate nazis is that hate? Or is it only hate if a nazi says I hate jews. Or an atheist says I hate muslim saudis vs muslim saudis say I hate atheists. Are they both hate? Or does it depends on your culture/position.
A simple unbiased AI would say they are all hate. And that's the problem. We would require humans to step in to decide what is hate or not. Which introduces other problems. A youtube saudi "moderator" would say atheists are hateful and ban atheist content. While a european atheist might say saudi muslim speech is hateful and ban extreme muslim content.
And that's how free speech dies. By trying to please and accommodate everyone, we drop ourselves to the lowest common denominator.