lots of great comments here already. I think it's true that some of the old masters were very dismissive of the lumpenproletariat and its potential revolutionary role, and a lot of the time it was essentially deployed as a moral judgement. it was often rooted in misogyny (even Connolly called women in the Magdalene laundries "lost women").
that said, I think it's a fairly standard part of the modern ML line that it's not a useless category as it does delineate distinct relationships to production, but we obviously recognise that the moral judgement and dismissiveness was regressive and can now be discarded. also I don't think the "criminal" aspect is inherent, feel free to correct me if I'm wrong but I think any disabled person claiming welfare essentially is in the category? along with masses of sex workers? which today encompasses a fuckload of queer people who obviously have a revolutionary role to play.