I know rehabilitation is different in Europe than the US, but there are likely resource constraints for attempting to do so at scale looking at trailing immigration volume.
Same story for the border closing in Finland by the way. You are dealing with a deeply unethical state, so when you don't let them in, these people will have to die. Because the other side knows that you are more likely to give in out of ethical principle.
[0] in last part: https://www.dw.com/en/migration-germany-to-deport-rejected-a...
(I'm guessing its generally asylum/refugee immigrants people are complaining about, not those from elsewhere in europe)
Refugees/immigrants/etc should be welcomed (I have sponsored refugees in the US), but violent crime must be prevented if someone runs out of chances. You need some recourse when you run out of options and people who have immigrated refuse to act in good faith. Immigration is a gift and a privilege.
I definitely want immigrants to integrate in our society (and am prepared to do this when I travel into another country). But I would not expect anyone to assimilate - which to my understanding means giving up their previous culture and take on the culture of the host country.