What if someone figures out how to make a similar factory very cheaply, and drives you out of business by only charging their marginal production costs for their widgets? The important difference, I think, is that they're using their own materials and electricity to make their goods, but people who engage in copyright infringement are too.

EDIT: And I'd note that many would would say that this second person is "Stealing the customers" of the first factory owner, but that doesn't mean what he does is actually morally equivalent to stealing.