Wealth enough to live comfortably is great. Anyone who works hard and saves should be able to have a nice home, cars, vacations, etc.
But, what we're talking about is wealth in the billions being concentrated in a small percentage of people. Those people then use this wealth (or at least can use that wealth) to gain power,more wealth, therefore more power, and so on. They can ruin ordinary individuals, have much more influence than their numbers would suggest on government action.
It's not about having money. It's about power, and power corrupts regardless of its source.