"the Imus remark... didn’t touch merely one third rail of American societal discourse (race) but two third rails (race and gender)."
Put aside the question of how there can be more than one "third rail".
I actually think that neither the race issue, nor the gender issue was key. I get the impression that Imus made a habit of standing on those 2 rails and laughing at the world. I think what he did wrong was to cast those sorts of aspersions on children.
Children are the true third rail of American politics.
Sure, college students are legal adults for most purposes. But they're perceived as not having entered the grown-up world yet.
If you want your career
To hit the skids
Just let folks hear
You're attacking kids.