Here is a little thing to spring on them if you want to have a little fun...
Imagine Adam and Eve had remained perfect, had 30 children who all grew up, and then one of those children "sinned". Maybe they decided to grab a little of the forbidden fruit, or broke some other rule. So is that child executed? Or allowed to reproduce and create little "defective souls" who now start running around the earth?
Its the same problem that will exist in the supposed "paradise". Once everyone gets sick of endless fruit platters and petting panda bears, they are gonna start breaking the rules of paradise. What then? Executions every day at sundown for the sinners? Some paradise.
They might try to fight you with the "we will be perfect" card. Yet Adam and Eve were perfect right? Perfection and free will are incompatible. You can only have one or the other. Eventually "perfect" beings will break the rules, unless they are simply robots programmed without free will.
JWs never think this through to the logical conclusion.