Bizarre as it sounds, I think a lot of people can hate on demand. Media starts beating the drum, and a proportion of the population go from apathetic to pretty damn frothy surprisingly fast.

Actually it doesn't sound bizarre; you are probably correct. Some people can switch to extreme emotions quickly and easily.

It wasn't socially acceptable to express your hatred, and there are a lot of people who just needed someone to stoke the flames of their biases to the point of hate and violence.

We've watched it become socially acceptable to not keep your biases unchecked and there is a multi-billion dollar media apparatus that pumps 24/7 propaganda into people's minds.

In the past, the stuff we've seen mainstreamed today stayed relatively niche on AM radio and in klan meetings.

2 things.

First, generally when people lives are good, they tend to blow the small problems out of proportion. This is pretty much how US got to where it is.

Secondly, if you look at the history of politics, conservatives have always been the ones to weaponize politics as a form of moral judgement. So nothing is really new.

I have a background in NLP (pre-LLM) and like to study extremist rhetoric, and, while I don't think you're being reductionist, it's a little more removed than that. I'd replace with "hate" with "problems and stress". Once you can attribute that stress to a group... that's when the hate develops. There are certain global powers who have recognized this and weaponized it. Agreeing with the most extreme of both sides, loudly, is the modern standard for propaganda.