The death penalty does not work long term as people will always gravitate to being oppressed and rebel against the setup eventually.

If you take the States for a example of how prisons do not work.
Half the prison population are mental health that is not getting dealt with.
70 million people have a criminal record meaning they can not vote.
These two facts alone lead you into seeing the system is set up for people to fail.
If you can not vote you can not hold impact on a community and guess who ends up in the system 2 out of 3 times as a male?
Slavery has not gone away,its just changed the way it did business.

Touching on the dynamics of race and crime,there is usually a up tick in crime from a group that has come from a place of persecution.
It goes away once they are established and have access and little road blocks to what every one else around them have.
In my community we have had influxes over the decades and it reinforces this thinking. In the 80s we had people from Vietnam.
90s where Indo-Canadians and recently Haitians. The gangs are always based on the last group to come in the door pushing out the group before them.
Once the roots are established people tend to not be of issue to the community.
So I think when you look at Europe you see some groups that never get established like the Roma and it makes the issue that much more glaring as generation after generation wander through Europe.

Just my thinking and its more thought than factual. So do not put my feet to the fire,just chewing the issue out in my head.