I think you're confusing a legal point (whether a T&C really gives Facebook any particular legal right in court) with the moral question of whether or not people should just roll over for large companies because of language we all, Facebook included, know that nobody ever reads.
Even if FB's T&C made it clear they could do this (something I haven't seen proven), that at best means people would have a hard time suing as individuals. They can still get upset. They can still protest to the regulators and legislators whose job it is to keep these companies in line, and who create the legal context that gives a T&C document practical meaning.
Even if FB's T&C made it clear they could do this (something I haven't seen proven), that at best means people would have a hard time suing as individuals. They can still get upset. They can still protest to the regulators and legislators whose job it is to keep these companies in line, and who create the legal context that gives a T&C document practical meaning.