Advocating violence against specific people is not illegal in the US unless it is likely to produce imminent lawless action. Saying "[racial slur] should be exterminated" doesn't rise to that standard. A live video saying "everybody get your guns and meet me at [location] - we're gonna slaughter those [racial slur]" probably does, but would be subject to safe harbor protections for the platform.
Libel also falls under safe harbor. The platform could eventually be ordered by a court to remove the content, but not until many people have had the opportunity to see it.
The question is every such business would need to face, including youtube, is where to draw the line. Child porn clearly is illegal and very few people would object to such a ban. But legal/not legal isn't always so clear, eg, what statement constitutes libel and is a given person enough of a public figure that less stringent standards apply.
Say I create a video saying "zcid lives at 123 Merry Lane in Westchester, MA. I'm not advocating violence happen to him, I'm just stating a fact." Is that legal? (Note: not only is the address made up, I double checked that no such address actually exists)
If there was a bright line then I don't think there would be as much controversy around the issue as there is. Pretending there is a simple solution (just ban illegal things and allow legal things) doesn't mean the distinction really is clear.