Ask Lemmygrad

All value comes from work, so any "passive income" source (including the stock market) which doesn't require active labor, technically means you are taking labor value created by someone else.

That being said, most capitalist countries allocate little or no social resources to taking care of the non-working population (IE the elderly, children, the sick, etc), and don't have democratic participation in deciding the allocation of social resources to taking care of these groups. Unfortunately that gives us no choice but to take part (on a smaller scale at least) in privatized retirement and health care plans. This forces us to learn finances in order to avoid a precarious existence later in life.

Of course in the long term, just like in the capitalist economy as a whole, class contradiction increase, and smaller investors are pushed out by larger ones, and like any game of monopoly, will end up with a single winner unless the board is overturned.

As long as we're doing what we can to overthrow this system, then we can consider stock investment as a minor moral failing, especially if we don't live in opulence, and just want a simple life. We should follow Engels' example, and work diligently for the overthrow of capitalism, live simply, and contribute what resources we're able to the communist cause.