I can't speak for everybody, but I'd say it goes back to what makes a liberal a liberal. I don't have any real desire to tell someone else how to do things - example I enjoy testing, diagnostics, analysis but chose to be an engineer not a doctor. Why? I prefer to deal with machines - they may be dumb and only able to do repetitive things, but they are honest, and I don't have to deal with how they feel. Doubtless that's not true of all or maybe even many conservatives.
Liberals, however, always seem to have to have victims to fix - gays, minorities, poor, non citizens who prefer living here ... I see teaching a lot in the same vein - it's a relationship dealing with power of a sort - to promote something in someone. Teaching can facilitate an understanding of math or of social values ... even turn a normal kid into a terrorist if so inclined. Every time I see a liberal I get the feeling that he or she sees something as not right and there has to be a fix for it - not to help that one person but a nationwide fix for anybody like that one person. You have to have victims or in your case someone to teach to make "whole". Of course there are teachers who are there to impart knowledge about the subject; you find them mostly teaching real science, math, engineering, medicine, etc rather than in the humanities.
