Facebook creates such an impression with the existence of closed and secret groups, private messaging and so on. Now, i don't take their promises of privacy very seriously because I know they could change the ToS at any time and have done so before, but I think the general consumer assumes that the contents of a secret group are at least somewhat secret - not necessarily enough that it would be safe to engage in illegal activity therein, but certainly inaccessible to anyone outside of law enforcement or FB engineers.

It's not very reasonable to insist that everyone conceptualize all assurances as blatant lies all the time.