> it simply means wealth grows slower, but still increases
But what does this mean? If you have a load of money in some companies, that's helping to fund their activities, and the companies' share price goes up a bit, you haven't gained any money. And you won't gain any until you sell some shares, which is already taxed.
They never sell their shares. They borrow against them, write off the interest, and then when they die, their heirs get a stepped up cost basis.
Rich people have been borrowing with their stock as collateral to access their wealth tax free for decades.
The debt doesn't just go away, and interest is paid on it. It's not "free". Etrade's best rate is 10.45%. If your stocks go bust, you're still on the hook for the margin debt.