One of the problems with the refugee admission systems in Europe is that if a refugee or even an asylum seeker turns out to be a serious criminal, you can't send them back like any other foreigner: either they might be in danger in their country of origin, or the return is for some reason technically impossible.
I think that the solution for this problem can and should be provided by the UN, in the same spirit of cooperation in which the countries accept refugees from the UN refugee camps.
The UN can establish a separate camp for the refugees whom their host countries have chosen to deport for being convicted felons. It should be separate from the normal refugee camps, and preferably far away from any local populations.
This should not be a punishment or prison camp. The idea is to provide convicted felons who have already served their time with a reasonably safe place to live if their country of citizenship is too dangerous to go to, and their habitual country of residence has kicked them out for being too much of a criminal. The standard of living should be about average for a UN refugee camp that's not in war zone. The residents should of course be free to leave at any time if they decide that their country of citizenship is not that dangerous after all, or if some new idiots decide to take them in.
I am sure this would greatly improve the goodwill of citizens towards the refugees.