Unlike caste in India, class as understood by marxists is not a fixed and inflexible division. workers can become capitalists and vice versa thru indiviual efort or folly. hence the rigid division of class is not scientific or valid.
What prevents all the workers to turn into entrepreners and make it big ? only a few are able to it inspite of severe hardships. G.D.Birla's grandfather was a ordinary worker in the 19th cent. now we have Bill Gates, N.R.Narayamurthy, Sameer Bhatia, textile barons in Karur, Thirupur, etc. all started with nothing and bare hands and made it to the top while their peers remained in their worker status. so what is the compasision ?
the term expolitation is a misnomer. huge population (which increases supply of labour to high volumes), govt deficts which erode real wages, high taxes, etc are major reasons for worker 'exploitations'
The organising power and the ability to motivate, manage and uplift a industrial unit cannot be quanitfied easily like the hours or amount of labour a worker puts in. Marxisim fails to understand this vital aspect of human nature. The drive and involvement needed to build up a business. hence most communist factories are less efficent and crumbled in the long run as histroy proves repeatedly. there may be exceptions where exceptionally driven and talented individuals, who were genuine communists (that is they are ready to put in their best effort for the betterment of the 'commune') create efficient eneterprises. For such efficency and sucess, all the palyers must be motivated to do their best in return for minimum salary (to each according to his needs).
the crux of the problem is 'from each according to his ability' ;without proper and logical rewards (as in a free market economy) such output of individual is simply not possible.
humans are ego centric and will put in their best efforts and drive only when there is a proper reward or profit.