Why should or shouldn't there be a wealth cap?

Simple; people can move and you can NEVER have a worldwide wealth cap, there will always be rogue states and even relatively powerful rogue states, to an extent (not saying this as a pejorative, I just mean they do their own thing) even Russia is one.

If you want wealthy to share more of their wealth, make THIS case as to why it’s in their interest, don’t FORCE them, who likes being forced to do anything? Exactly.

Power vs force, power of logic, emotion and action vs FORCING wealthy people to do things. Force never works for anything.