David Neiwert (aka Orcinus), has some very interesting and disturbing things to say about the sad and vicious state of political discourse. Start with his The Political and the Personal, then read his summary of the many reactions. The purpose of this essay isn't to agree or disagree, so much as muse aloud in his wake.
I don't personally have a formed view as to the psychology of either the modern brownshirts or of their fellow travelers. As Sinclair Lewis brilliantly explored in his vastly under-appreciated novel It Can't Happen Here, many of the people who go along with brownshirts do so out of simple opportunism. Which is why the Republican party's actions that seek to entrench their political victories economically by taxing Democratic-voting districts and transferring money to Republican-voting ones is for me as least as worrying and cynical as anything they say. Similarly, the strategy of imposing today's costs on tomorrow's citizens (huge deficits that are not spent on investments likely to repay their costs) presents a serious problem; were there to be a serious economic repercussion — like OPEC going off the dollar, or world markets choosing to hold more Euros and sending back a chunk of the dollar overhang, then we'd see the true cost of this fecklessness.
I am not quite as persuaded as Orcinus that today's political rhetoric is that much worse than what I recall from the early 70s—or even that much more respectable than invective was then. Seems to me that I remember Nixon, Agnew, and a bunch of other politicians and commentators were fairly vicious towards Vietnam War protestors. And some people acted out then too. It was bad then, it's bad now, but what seems worse today isn't the rhetoric so much as what it covers up or distracts from.