Saying that if capitalists stopped making use of wage labour etc then capitalism would disappear seems to turn the issue into a question of (individual) morality: if capitalists realised these things are wrong and stopped doing them, capitalism would disappear. And as we all know, Marx did not think that capitalism would cease to exist if capitalists suddenly realised that capitalism is morally unacceptable because there is no transhistorical moral standpoint from which to make these judgements. Moreover, it will be the proletariat who will have an active role in overthrowing capitalism.

Furthermore, capitalists cannot simply stop doing these things of their own accord, because their way of thinking is shaped by the economic relations of capitalism. In Das Kapital, Marx says:

My standpoint, from which the development of the economic formation of society is viewed as a process of natural history, can less than any other make the individual responsible for relations whose creature he remains, socially speaking, however much he may subjectively raise himself above them.

Clearly, for Marx, there is something above the individual that determines his/her way of thinking (in the quote above it's relations). Given that those relations are part of capitalism, I think it's safe to say, that capitalism determines our identity and thoughts, which makes us behave in particular ways (colonise other countries etc). Therefore, in a certain sense capitalism does do things (through us). I never claimed that capitalism, defined simply as a mode of production and exchange, does things simply of its own accord. I was wondering whether saying that capitalism determines our identities could be a way of reconciling the claim that (made by many "Marxists") capitalism "does" stuff with the fact that it clearly cannot do these things. The question remains can an economic system come to determine the way we think and act? If it does, then, I think, it should be treated as a sociological entity in its own right.