I think the closest thing Ellis to what you're proposing is Guantanamo Bay. I don't think we can say that's helped. But we can't really know. Or perhaps the crackdown in the Philippines now under Duterte - will have to see how that pans out.

The other thing with a policy decision is it's also about how things are perceived. The way people think about a policy can be far more important than the details of the policy itself, and that needs to be carefully considered, if there is a possibility of doing more harm than good. Not saying that conclusively, but it might be why they haven't done what seems to be 'common sense'.