[quote=@Andreyich]
Why let in just a bit of a problem when you can let in none of it at all? 
[/quote]

If you vet potential immigrants properly, you minimize the risk of admitting future murderers -- and then you get to add some real brains and goodness to your list of national resources. Good immigration is an asset. Uncontrolled immigration, poorly vetted immigration, illegal immigration -- these are what cause problems. Just ask Francistan.