I would say that nine out of ten Marxists/revolutionary socialists/Trotskyists are middle-class.
Most academic Marxist writers and activists belong to a tiny and severely circumscribed social milieu: the university. What's more, the higher up the echelons you go in the leadership of the Left, the more likely Leftists/Marxists are to be upper-middle-class (e.g., the leaders of Leftist parties, lawyers, “rights activists”,professors, journalists, etc.); rather than plain middle-class ("petit bourgeoisie").
Marxists are the perfect subject for a sociological analysis; though since many sociologists and “class analysts” are Marxists, such a thing has never happened.
What Marxists seem to say is that it's okay for them to analyse where non-Marxists/Leftists get their views from (i.e., their "class position"); though it's wrong for people like me to analyse where Marxists get their ideas from (i.e.,their class position).