You are not wrong there. But what´s your suggestion? Do you want to check/control every posted/to post meme on the platform? You cannot blame a platform for providing a place to upload things there.
I am not going to check/control every posted meme on the platform, because even if I will or did, there's nothing I can (or will) do. The problem that might arose is between the original meme owner (e.g. Sammy Griner "the success kid" or Laina Morris "the overly attached girlfriend") and the meme poster.
As for my suggestion, obviously is not to try earn through the platform, especially as the platform already confirms (and wash their hand of) the legal implications and most likely won't assist you when it really comes down to the court. Posting on 9gag or IG is probably a light case because you didn't get any money through it, thus the legal infringement (maybe) is lighter. Posting with the aim to monetize a copyrighted content, though, is a whole different case.