I'm quite happy for people to think Jill Stein is horrible, her campaign was counterproductive to "The Left" (however defined), and that people who voted for her are idiots. It's a bit more nuanced than that, I think, but fair enough. But I see a lot of "well if you add Stein's votes to Clinton then Clinton wins so she's just like Nader" exercises. It generally takes ignoring Gary Johnson's votes or using some combination of creative accounting and blaming (he took votes from Clinton too so he gets some of those but it isn't his fault like Stein's!) to get there. The question is, in a world where Jill Stein (or another Green party nominee) didn't run or if in September Stein had implored all of people not to vote for her but vote for Clinton instead, would Clinton have won? I don't know, um, maybe? I mean, people can have opinions about that but just moving vote totals around doesn't actually answer that question. If no Stein, would we be crediting Johnson for Trump's loss?
Again, I don't have any interest in defending Stein. Boo Stein! But I don't think it's clear that absent Stein, Clinton would have won. More importantly, so what? Presumably we're going to have 3rd party candidates in every election. You can think they're assholes and that people who vote for them are assholes, but that doesn't make the candidates go away or their voters vote for the Democrat. For various reasons I do think Nader was actually a spoiler candidate, in part because he got an immense amount of media coverage (when does anybody on the left get an immense amount of media coverage?) But generally...just a fact of life. Can't wish them away, and can't assume their voters would vote for you even if the candidates didn't exist.