How should we treat Facebook and Google?

For most of the history of U.S. antitrust law, the rule has been that the government's role is to protect consumers, and that means increasing competition so that they can get better prices and better products. However, in the age of Facebook and Google, their products do not cost money and consumers seem pretty satisfied with them. Even so, political candidates and others have said that Facebook and Google need to be split up into smaller companies because they are too big and have monopolies in their industries. Do Facebook and Google pose a threat to the competition? If so, how should we treat a company that provides free products/services and that consumers seem to use willingly? When could that be a bad thing?