[wtallis]

What would be at Facebook's discretion? Are you suggesting that their TOS could dictate what web browsers you're allowed to use to access Facebook, or whether you're allowed to store and make other personal use of the information they send you?

It's impossible for something like Facebook to use a whitelist model for determining what you use to interact with their service, and they can't retroactively add things to their blacklist. They usually have to rely on generic rules about causing harm to the service, but then it's no longer a pure whim.

[cbsmith]

No, I'm suggesting that the TOS could dictate that whether you are allowed to do it or not is entirely at Facebook's discretion, and they could choose to say that it isn't okay.

A lot of software licenses have a clause that basically allows the licensor to revoke the license on a whim.

[wtallis]

Facebook can always give themselves the option to unilaterally decide to no longer serve you going forward. But that's not the same as Facebook being able to declare that arbitrary behavior is retroactively in violation of an open-ended clause of their TOS and therefore grounds for lawsuits and CFAA prosecution.