Rich people being rich is fine. Them buying luxuries for their money or gambling (casinos, stock market, startups) does very little harm and even some good because some of their money comes back to other people and few of them do something good with it.
The problem starts only when their money touches the parts of economy that are shared by other people because they drive the prices up by buying large amount of stuff and hoarding. Things like property or food or raw materials or land. We just need to make those activities unprofitable for them.
And the problem with immense wealth is not raising inflation or anything like that, that is market stuff that will correct itself. The problem is buying your way into policy control, and people/corporations that are so powerful that not even the law dares touch them.
And even the case you linked to, very wealthy people are much less likely to be charged with these kinds of crime as well.