If you are aware of and have direct access to information vital to stopping child sex trafficking, you must share it when legitimate authorities request it. There's no message board syllogism that is going to get you around that, which Durov is finding out.
This is the issue. People think freedom of speech, association and expression means I get rights to say whatever I want and no one should be able to treat me differently.
Well, not exactly.
Firstly it only applies to government not being able to stop you from speaking. Secondly, it in no way precludes the government from taking necessary actions to stop what you're speaking about. So these pedophiles out here can talk about their, "hobby", to their hearts' content. But government can and should use that information to investigate, interdict and prosecute any illegal activities in which they are involved.