To rely on the argument that as long as there is welfare and the risk of crime, there must be “immigration control” is a really poor argument.
You could justify almost anything that way.
As long as there is rape, there must be mandatory chastity belts.
I could go on like that all day. You can’t justify one evil by the existence of another evil. You’ve got to respect rights. Perhaps that will solve the problem you claim to be concerned about. Maybe it won’t. But at least you’ll stop being part of the problem.
The solution is NOT to violate people through violating property rights (which is what “immigration control” comes down to), but to STOP violating people through stealing their money and redistributing it, and by criminalizing self defense.
The reality of the existence of evil doesn’t justify more evil. Get rid of the evil you are using to justify a second evil, rather than looking to a second one to counter the first. Or, at the very least, stop defending the root evils as an excuse for the secondary evils.