Imagine if Ant and Dec had racially abused a colleague before lamping him. Would there be a big political campaign and a million-strong petition to save them? I'm not sure. This tells us that Clarkson's popularity isn't based solely on the fact that he's a talented TV presenter.
Equally, though, I'm not sure that its due simply to the fact that he is (or plays at being) an obnoxious racist bully; whilst he has the support of many prominent arseholes, his popularity isn't confined to bigots.
Instead, I suspect James is right: Clarkson is popular because he's a "rebel." When he uses words like "slope" or "nigger", his supporters don't cheer his racism but the fact that he's rebelling against then"PC brigade." Many men believe as Bruce does: "we are not allowed to think or say what we want to any more, the thought police have taken over." To them, Clarkson is a hero not because of his racism so much as his fighting for freedom.
How did we get into a position where a millionaire public school racist bully can be seen as someone who speaks for the underdog?
There are two things going on. And I don't like either of them.
But on the other hand, there is a big dose of illiberalism on the left - seen, for example, in its policing of language; the urge to ban things; and in New Labour's creation of thousands of new criminal offences (something which the coalition continued). And there is a particular type of careerist who uses feminism and "political correctness" to sustain their own narcissistic self-righteousness and ambition: for example, when Greg Dyke complained that the BBC and then FA were too white, he did not see either as a reason to resign himself in favour of a black person.
These twin positions are in danger of crowding out a third. This is a leftism which believes in free speech - which accepts (grudgingly) Clarkson's right to use retrograde language but also others' rights to call him a cunt for doing so: a leftism which worries about real, substantive inequalities more than about language; and one which wants not so much to get women or right-thinking men into positions of power and wealth but rather to abolish such positions.
In these ways, the Clarkson affair has highlighted the poverty of much political discourse.