I think that alone — meritocratic success — would explain the leftist when it comes to generosity or sociability. Why collaborate, etc, when you have a track record of beating everyone else in the room?
However, my own experience (when it comes to gregarious, polite, etc; I don’t know about generosity) has been mixed. Liberals and leftists tend to be more asshole’ish on the net. But much better in person. I think the context (of live encounters) tones down their MENSAssholishness. Conservatives on the other hand vary… one type, the kind old church lady prone to saying sweet racist shit fits your stereotype. Then there is the old Irish guy I met at a barbecue recently, who took off at the first excuse on that “socialist faggot”(*) Obama.
FWIW,
—ravi