Why do we allow this?...

I agree with you about making it harder, Pete. But it's not that simple anymore. Look around you the problem is already here as I said. We need to solve our own bias and fear to solve that of other peoples and cultures. We have to state quite clearly that other cultures, whether religious or secular, have to integrate and comply with the laws of this land. We as British Citizens have to do precisely that when we reside in other other countries. Any person of whatever nationality who has immigrated to this country and commits a serious offence should be deported back to their country of origin after serving whatever lawful punishment has be passed on them. Pleading that their home country would not be "healthy" for the person should they be returned should be met with the retort "You should have thought of that before you committed the offence" But we should still recognise, but make it harder, for those people fleeing their country for their lives should be able to find refuge.