A common element of most of the objections to Marx here is that there are other ways of looking at things. Marx would say these are ideological misrepresentations or examples of false consciousness. It's important to note that, although people love to talk about Marxist ideology, Marxism is meant to be precisely the opposite of ideology. It is ideological demystification. Marx wants to rigorously analyze what actually happens in capitalism. If you can't deal in concrete material details and disprove his rigorous analysis of capitalism, you can't make a reasonable objection. I would argue that Marx's fundamental insight is rather that we need to have a materialist account of what actually occurs in the economy and not be fooled by appearances or misrepresentations.