User blog comment:Kaido King of the Beasts/Vegapunk: Friend or Foe?/@comment-24850639-20150713184205/@comment-24.235.56.170-20150714001737

You're pretty spot on there. But I think you're wrong about one thing: they don't need to blackmail him. Vegapunk cares most of all about researching Devil Fruits, and things related to them.

Basically all of his major advancements have been DF-related; created lasers by studying Kizaru's DF powers, came up with a way to cross the Calm Belt by studying sea prism stone, created artificial DF's. Not to mention all the knowledge he's accquired about the nature of DF's themselves. These things aren't necessarily dangerous on their own, but used by any military force, they are a deadly combination.

My point is this: researchers require resources. All the Navy needs to do to keep him in one place is supply him with anything and everything that he needs. Cover the island with guards and he probably wouldn't even notice, since he would be too engrossed in his research. The only thing they need to do is keep his whereabouts secret and guard against pirates that might stumble onto his island accidentally. And in return, they get access to all of his discoveries and are able to weaponize them as they see fit.