I do not think it is the money that made them terrible. I know all sorts of terrible people that would do the exact same things. The only difference really is they do not have the money to execute on those ideas.
Money does not make you a good or bad person. It just makes you more of who you are already.
Of course the money doesn't make them terrible. Being terrible makes them money. Lots of money. There aren't really other ways of obtaining so much money, which is why if you see someone that has that amount, they should be viewed with suspicion.
I specifically did not say money makes them mentally ill, but rather the type of person that seeks to hoard so much wealth that they have billions is correlated with mental illness.