I literally cannot figure out any sane or rational reason for this.
Multiculturalism and diversity foster a divided society of competing factions, making them much much easier to Control. The last thing any Tyrant wants is a Unified Country of Like Minded Citizens, they CAN NOT be Controlled easily for they have the ultimate power when Unified.
See Divide and Conquer.
Our enemy, the enemy of our souls, loves chaos and mayhem and not peace. He is working hard in current times.
If they had not done the same thing for Jews fleeing Germany, who knows what could of happened. </s>
More than anything else tyrants cannot tolerate an armed populace.