> That fatties should just have to exist until they can make the identity level genetic changes on their own to lose it.

Or just eat less and exercise more..

What happens when they come off of this drug? Does the weight just go back on again?

Underlying lifestyle changes are the proper way to lose weight and keep it off. The sort of lifestyle changes that most non-fat people have been making all of their lives. That's why many people criticise shortcuts like this. It's a lazy solution to (mostly) laziness.