We already have marginalised (not sure how you define that) young men who live in our urban areas and commit crime.
That does not mean that other young men, who may have grown up in some of the most violent parts of the world, and/or have been brought up believing that women, and especially Western women, are all scum who are there to provide them with sex, do not on average commit more, and more serious crime. They are certainly more likely to be marginalised than the young men who are originally from London.
Looking at Germany again, the figures show that North African men commit a very high number of crimes. Apparently a lot of young men from gangs in North Africa migrate to Germany. That explains the culture of crime that they bring with them.
Is it a good idea for us to be adding to our current crime problem by welcoming more young men, who are far more likely to be marginalised (if only because of the migration experience, without their families, etc), and who will often bring a higher crime culture with them?
We need an immigration system that works quickly and efficiently. If the question is how to persuade marginalised young men who when they reach the UK are too old for the education system not to commit crime - well, what would you do @Gealach ? Assimilation into the UK classes? English language classes? Encouragement to join football clubs etc? Further education classes providing training towards jobs? With the stick of not being allowed to stay long term if they commit anything worse than a minor crime?