Ok so I've looked into various sources, and it looks like the police is concerned for the safety of ppl at the DiEM as well as civilians around it.

Because of that, they prohibited specific inflammatory and incendiary words and language as to prevent the discussion from escalating into violence in Berlin.

Listening to some of the things that were said before they issued the ban, it is clear that some of the speeches were radical or very much pushing the envelope.

Now there is some confusion about where the ban on specific language came from - police refers to the Senate, Senate refers to other parties (and that's not great), but it's not as if the police just felt like it or as if there was some shady stuff going on behind the scenes.

I am a German from Berlin, so I am very concerned when I hear stuff like this, and that's why I had to look it up and dig into it to some degree. I wish the international press did a more thorough job, because if it didn't take me that long to find a different account, that means they didn't do their job and I don't like that.