"Redistribution of wealth" is a clumsy way of trying to oversimplify a larger concept anyway. I think most of us are advocating for a system where labor gets its fair share of the spoils of a capitalist wage labor system. We don't have to exist in this kind of economic system, but so long as we do, the accumulation of enormous wealth by a few individuals is undesirable. If you're accruing massive wealth you're taking something from someone you owe it too. So either you owe it to the government so they can distribute it, or you owe it to the people who worked for you.
No capitalist accrues his wealth on his own and in a vacuum. It happens because somewhere in the system someone or some thing is being taken advantage of.