It's not violence that's the real issue with Clarkson, it's racism. Yes, he ultimately got fired for doing something violent, but not on TV. If you say something (that could be interpreted as) racist on a mainstream US TV show there is also a backlash. E.g.:
There's a huge difference between being considered a "serious" TV personality and an "unserious" one, and what your public image is.
And even then, it depends on audience. FOX News personalities express far worse sentiments daily and mean them than Clarkson ever has. Their audience is fine with that.
Paula Deen was supposed to be a nice upstanding older woman showing people cooking. Even the claim that she might have used a racial slur in the past torpedoed her career.
Clarkson's public image, and one that he intentionally curates, is one of being bombastic and politically incorrect. He can crack whatever jokes he wants without it going to hurt his career in the US. In some respects, Howard Stern might be a good comparison of someone with a fairly similar type of image.
There is no comparable mainstream show in the US with a presenter as openly racist and offensive as Clarkson. Nor could there be, because they would be fired (as my and your examples show). I wouldn't necessarily say that the US is "less racist" than the UK on the whole, but to the credit of the former, it is hard to imagine a US show about cars being presented exclusively by openly bigoted white dudes.
I've yet to hear an actual propf of him being openely racist. There was that outtake never shown on tv when he said thw n word as part of an old rymhe that was what it was.
Can't find much more beyond that. Some wanton racism on their trips, played on stereotipes and misunderstanding, but critiquing vietnamese cousine or italian way of driving doesn't sound openly racist.
http://www.theguardian.com/tv-and-radio/2015/mar/13/univisio...