Noting that some significant portion of the anti-Semitic threats made in the recent past were perpetrated by a left-wing journalist, Kevin Williamson puts his finger on the impression that many conservatives (and, I would hope, clear-eyed moderates and even liberals) are getting: 

The Left, for the moment, cannot seriously compete in the theater of ideas. So rather than play the ball, it’s play the man. Socialism failed, but there is some juice to be had from convincing people who are not especially intellectually engaged and who are led by their emotions more than by their intellect — which is to say, most people — that the people pushing ideas contrary to yours are racists and anti-Semites, that they hate women and homosexuals and Muslims and foreigners, that they could not possibly be correct on the policy questions, because they are moral monsters. This is the ad hominem fallacy elevated, if not quite to a creed, then to a general conception of politics. Hence the hoaxes and lies and nonsense.

Phony hate crimes. Phony hate.

“Play the man.”  That is, rather than try to move the ball down the field, hurt the other team’s members so they can’t make any progress, either.

Of course, contact sports have, well, contact, and sometimes it’s difficult to tell how clean a play is or whether a player is going after his or her opponent or merely standing his or her ground in the face of aggression.  In policy, the important judgment for spectators is where the emphasis seems to be.  Charts and analysis coupled with a bit of roughness is very different from accusations designed to keep people from considering alternatives to one’s preferred perspective.