They lack the confidence to discuss civilly the merits of their own opinions and lash out with insults at people who think differently. They always attack the intellect and motives of those whom they do not agree with. It's so interesting too that these progressives see no problem with proclaiming themselves as perfect models of tolerance. They remind me of the saying that there are only innocent men in prison (in their minds, of course). With liberals we now have the least tolerant people claiming they favor diversity! We have people who call anyone who doesn't agree with them a fascist, yet they, well they're the high priests of pluralism, a special pluralism where we all agree.
Their greatest fear is that people will realize that everything proposed by Democrats requires massive transfers of wealth before anyone realizes it was done for votes and power rather than the general welfare.