Coil:
I am a strong believer in creating a Gangstas Paradise on an island and if you commit a crime like sexual, homicidal or aggravated violence you lose all forms of citizenship all over the globe and get permanently banished to said island to join your fellow criminals and live in the ranks of their society. If they kill, rape, torture or vandalize any of their buddies literally no one cares and its no ones fault.
I'm not entirely opposed to that, but how do you ensure they don't escape, and who pays for the infrastructure? Seems to me just shooting them all up front is safer and cheaper for the taxpayer.