This is what this disagreement comes back to though. This was an assertion of Marx's, which he proved to his own satisfaction, and to the satisfaction of some other people. A hundred and fifty years down the line, when revolution as he described it has not happened, and what revolutions did happen did not abolish capitalism, and the 'working class' is no closer to a revolutionary position in the UK than in his time - in fact considerably further away - do we not reassess his ideas at some point?
For me the useful thing to take from Marx is to examine the material forces in society, particularly against the idea that society progresses mostly through new ideas or enlightened leadership. Shouting at everyone that MY VERSION OF CLASS IS THE ONLY RIGHT ONE and getting upset at people who fail to 'understand' what class really means (we understand, thanks), is achieving what, exactly? Maintaining a blind faith in one person's depiction of society, against 150 years of consequent evidence, as far as I can see.