Imagine a random, un-nerdy German, entering "www.facebook.com" into his browser, and getting a themed page, written bij Facebook, about how DT is effectively blackmailing them. Note: Facebook controls what this person sees, not DT (theoretically of course they could modify the page but I doubt they're that evil, even if they were fast enough).
If Facebook does some effort to write up a decent piece of text there, then I bet most people would root for Facebook, not DT, in this case. Especially so if the mainstream media does not explicitly appear to disagree. In fact, papers like Bild will love a healthy scandal and will likely choose Facebook's side just to blow things up. (idem for Google, of course)
Ironically (or not, and I missed your reference) random, un-nerdy Germans already fight with Youtube videos being blocked and are faced with a similar message very often [1].
I see at least two problems: the leverage that the other party actually has (GEMA, DT) and the willingness of the citizens to do something about it.
If Facebook does some effort to write up a decent piece of text there, then I bet most people would root for Facebook, not DT, in this case. Especially so if the mainstream media does not explicitly appear to disagree. In fact, papers like Bild will love a healthy scandal and will likely choose Facebook's side just to blow things up. (idem for Google, of course)