We have two "monopoly" problems here... the legal, and the political. Even for companies that are probably not legally monopolies, like Facebook, consumers are

We have two "monopoly" problems here... the legal, and the political. Even for companies that are probably not legally monopolies, like Facebook, consumers are very uncomfortable with them, and politicians are leveraging that consumer fear. So if antitrust doesn't work, think about where politicians might turn next. Or they may just go on making blathering promises with no intent to keep them, like they do about, say, Citizens United.