It’s an old meme the left has been pushing for some time… that they’re just pragmatic, realistic, and based on social science while their opponents are ideologues… or worse nonthinking reactionaries (racists, sexists, et cetera).

It’s really important to their internal worldview and [self] justification for their actions. To this end, they often really believe it (i.e., if it were not true, then what good are lefties really doing fighting their fight).

It’s also important to their external movement in order to hide all the nuts on the left / maintain the no enemies to the left status quo. If they’re all pragmatic realists and such, then all those socialist ideologues they work with are just boogie men of the right wing imagination. On this level, unless they deploy a lot of doublethink, I doubt even they totally buy it. I imagine they just avoid thinking about it. But, because of their cultural hegemony in certain sectors, they can just laugh off people who bring up lefty ideological issues (example: “pragmatic centrist” Obama is ruining his political career in favor of pushing for the socialist goal of forced equality in health care… once you tear down the various healthcare talking points, leftists fall back on ‘fairness and equality’ as their goals in healthcare reform… but if you bring this up in the wrong place… ahem… you get the picture…).