Um, tough, if you want to be a billionaire, you get to sell a tiny fraction of your assets to pay taxes. If they don't want to sell assets, they can pay themselves a larger salary or something. Or, like you said, take loans which is literally what they do to afford their lifestyles, just use that for taxes. I don't really care which.

"Taxing the rich" is literally solving the thing that is a problem today.