How do you teach such norms, on small things like shared fruit trees, to adults? Which entrepreneurialisms to encourage and which to stop.

That is incredible difficult and basically boils down to resocialising people in another culture.

In the case of refugees we are facing the additional problem, that some originate from areas that are long time disfunctional, resulting in humans that never before have been socialized in a working society.

I believe that an important factor is to mix newcomers and locals, unfortunately that goes against the desire of both the government and the immigrants. Both want to centralize for efficiency resons.

when german people get free fruit: yes, that is well and good, the way the world is meant to be.

when non-german people get free fruit: aaaargh the immigrants are eating all the fruit! no respect for social norms! poachers! thieves!

Actually yes. Ingroup preference is a good thing.

Why is it a good thing?

Because it lets them feel good about themselves.

I love this new right-wing "intellectualism". They just declare "actually, racism is good" and then derive everything else from there

Nothing racist about preferring your ingroup. The arabs have a really good saying when it comes to this: Me against my brother. Me and my brother against my cousin. Me and my cousin against the world.

Why so?