Blocking those tweets is not a violation of the principle of free speech. At least not in the legal sense. Private people and companies suppress speech all the time and that's fine. It's when your government does it that it's very wrong.
The difference between censored speech in Germany (or America: we have limits on free speech, too) and someplace like China is German society has agreed to limit certain offensive speech where as Chinese citizens don't really have a say in the matter.
Users can be creative with what they want to express with this approach - with no Twitter at all, where is the wiggle room?
Twitter isn't doing this just for fun, they're doing it because of the policies and laws of the countries in which they operate.
If Twitter told it's users that they couldn't post bad things about Jack Dorsey that would be different.