Also -- aside from the question of what workers produce value, there exists that immense 'pol' of activity which (while dependent on capital in one way or another) goes on outside of exchange: cooking one's own meals, doing one's own laundry; doing laundry for the entire family. Some feminist scholars (at least in the past) condemned Marx for not ascribing value to household labor; that is an incorrect criticism since such labor (or the labor of tying your own shoe laces) simply lies 'outside' the capitalist relation.
The weight of non-capitalist activity in capitalist society is (among other things) one of the reasons there cannot be a "science" of economics.
I'm breaking off here, since Chris's reference to Marx on crime led to a fascinating lbo thread that I am still studying.
Carrol