The most convincing argument I've heard for voting third party instead of for Genocide Joe is that liberals were more politically engaged and had more of an activist mentality under Trump.
Also, I've given consideration to the idea that "vote blue no matter who" types would likely vote for a more leftist Democrat than the ones currently being offered. In a long term strategy, if leftists refuse to vote for Democratic candidates who are too far right, then the Democrats would have to either try to appeal to the Trump demographic (which they do unfortunately do), or appeal to the leftist demographic until they get the leftist votes back.