Why is it wrong to take pleasure in the misfortunes of others?

[Tellos Athenaios]

I sense circular logic in the moral argument.

For this to cause further negative behaviour, then the original action must be percieved as negative. Ie. one bad things makes further bad things happen. But then we have just assumed that the action is bad, we haven't made any arguments as to why it is bad.

What? The moral argument is about wishing unto others, not about what certain behaviour might lead to. The latter is just a practical application of hard earned lessons handed down from parents to their children in an easy to digest rule of thumb: don't do it, it's really better if you don't.

There is no reasoning in there at all, it just so happens to prevent actual bad behaviour. It's not bad because it's bad, it's bad because the stigma of bad triggers the self-control parts of your brain in any well adjusted person. That, in turn makes you avoid doing the really bad stuff.