Geez... I keep thinking about this.  I don't know if the original post is real or a hoax, but I have heard similar arguments in other places.  The line that keeps getting me is "God doesn't need a reason to punish you."  That's not a new idea, and goes back at least to the Puritans, and probably farther.
It's another case of not thinking the idea through.  If a parent punishes a child without reason, we call it abuse.  My father did that do my brother and to me.  We left.  He died without seeing either of us again. 

But, beyond that, is the idea that "You're bad, so you must be punished."  This rationale, carried to its logical extreme, led to the Holocaust.  The combined idea that people can be instrinsically evil, and that evil must be punished leads inevitably this way.

I'll address punishment first.  What is punishment about?  What's it for?  It is meant to modify behavior.  A parent punishes a child for doing something dangerous, because they really don't want the child to do that thing again.  A city punishes you with a fine for parking in a no parking zone, because they really don't want you to park there.  It's about changing what the person being punished does.  Therefore, punishment has a reason, a purpose for the target of the punishment.

Now, intrinsic Evil.  "Badness" as a physical trait.  I have trouble even picturing it.  I can understand bad behavior, maybe even a habit of bad behavior, but "badness" as something inbred?  How would someone observe this, how to you measure it?  Surely such a creature would never be able to do anything good, even by accident.  Would undesirable behavior count as Evil, or just destructive acts? Is playing loud music at 2AM evil, or just rude?  Is rudeness "bad", or just annoying?   It's a nonsensical concept.  And, it is not the basis of the concept of Original Sin.  That concept is not that "Man is naturally evil", it is the concept that "Man is flawed, and therefore bound to screw up.".  Original Sin is the idea that, no matter how good we are, we will sin from time to time, because we're not perfect.   So...no person is just naturally "bad".

But, for the sake of the original problem, let's suppose that it's possible.  Here is someone who is just naturally, by the fact of their existence, Evil.  Will punishing them change that?  If they are innately "bad", can they change their behavior?  NO.  Punishing a lion for eating meat will not make it a vegetarian, it will just make it a neurotic lion.  So, is there any point to punishing someone for their innate sinfulness?  No. There would be no reason to think that punishment would change their behavior.

The only reason to do something like that would be an evil reason... creating suffering for selfish personal gratification.*    I think we can all agree that doing that is BAD.

*BDSM is a different dynamic, it isn't selfish, for one thing.