I have no idea where you're getting this from. Saying someone is a Lumpenprole isn't a moral judgement, just an economic one. Someone who grows rice and the bandits that steal it have different relations to the means of production. They are not just proles who break the law.
it's ridiculous to try to carry that notion forward to the age of cell phones and heavily armed maoist prostitutes
Engels was largely revolutionary but he was also bourgeoisie, that does not mean that the bourgeoisie as a class are revolutionary. Also, many ML theorists argue that Lumpenproles do have revolutionary potential while not denying they exist as a class.