Diversity is another form of death by socialism. Affordable socialist payoffs just aren't good enough for whites - they want all kinds of expensive gibs. Imported SAmer peasants and Muslims? They'll trade votes for the gibs that whites can generate. It's socialism arbitrage.
If you can do that you don't need to sterilize them. They'd be guests and leave when the contract is up. Their children wouldn't be citizens. Their sponsor would be financially responsible for their crimes and torts. A country that could do that would look very different.