This is why, throughout the Torah, the injunction to give justice and hospitality to the widow, the orphan and the foreigner is repeated over and over again. Because the health of the whole society depends upon it.
Two reasons. One of them says that our memory of who we are and where we came from is to be found in these people on the edge of the social sphere. The other says that the holiness of God is to be found with them, in that place.
When May creates a 'Hostile Environment' and Duncan Smith pushes through Universal Benefit, the one to create a bad place for foreigners, the other to make the poor pull up the socks they don't have, they are flouting this law.
And when that happens, the whole country suffers. Because it has ignored or pushed aside or denied the memory of its own history: that we were once foreigners and were given a home. That we were redeemed. That God is holy.