Most of Breadtube I thought started as "anti-alt-right" types, a bunch of them came out of that whole Atheist/Skeptic movement that had a few years reign. I think this was common for the "alt-right" too, but one group went right and the other left, even though their main thing was to just fight culture wars more than anything.
The "dirtbag left" are "actual" leftists (aka socdem, but some communists, tankies, etc.) who just don't agree with the PC/SJW culture war crap. (aka BOTHSIDERS as they'd make fun of Jordan Peterson and people like incelsiorlef)