Is that some sort of misplaced arrogance, or do you really not understand how easy blocking WhatsApp/Facebook would be if the German authorities wanted to do it?
People write as if the Internet is some huge network that everyone has unlimited access to, but guess what? It's not. You have an ISP, and somewhere up the line they are hooked in to a relatively small number of pipes in and out of any given country, and those pipes are controlled by a major infrastructure provider that isn't going to argue with the national government.
The political fall-out could be a different question, but somewhere like Germany the people are very cautious about excessive surveillance and profiling for obvious historical reasons, so I wouldn't bet on WhatsApp/Facebook winning the PR battle either.