Absolutely some humans convinced some other humans! Enough, in fact, to make change! I'm not at all trying to avoid that idea. But I'm wholly unconvinced that when those things went away, a majority abandoned their racist notions. Rather, the next generation, when raised without the same degree of racism surrounding them, didn't take up those ideas to the same extent. It's not so much that people were convinced "I need to stop being racist" but rather that a subset was convinced "we can't teach this in our public schools"

That's all just observational though. Around here it's not so much racism against black folks but rather against aboriginal folk (and to some extent, middle eastern folks). I hear almost none of that crap from my generation or the younger generations, and still hear horrible amounts of it from older generations. Yes, some people in those generations changed, but it sure seems like the "racism rate" is significantly lower than the mean in the younger generations and significantly higher than the mean in the older generations.

Edit: it's also quite possible that it hasn't gone away in the younger generations either, it's just not considered something that is acceptable to say in polite company.

Edit 2: and thank you very much for making me think more about this!