One way to stop that is to get rid of the step-up in basis on inheritance, or modify inheritance tax to be on a similar level to income tax.

Or make loans against stock value a taxable event.

Billionaires seem to be quite skilled at avoiding inheritance tax. They have avenues for passing on generational wealth besides what most people imagine as passing it all directly via a will. For example, they can create a corporation that owns and manages their vast assets, and then transfer control of that corporation.

Or even just saying "loans above $N are a taxable event", and make that value like $500,000. This would allow like 99% of the population to actually borrow against their stocks in the case of an emergency without having to liquidate their stocks or be punished for it, but $500,000 is nothing for a Bezos or a Musk.

This would only stop borrowing via loans that are collateralized by stock assets. These banks would presumably still offer uncollateralized loans to these folks (you have $X billion dollars, I'm confident you'll be able to pay off a loan for 2% of that, here you go, no collateral needed). Then, the end effect will be slightly riskier loans for the banks, and slightly higher interest rates for the billionaires.

And if you set the limit at $500k, you're going to block rich, but not super rich folks from taking out loans to start new businesses, etc. To me it seems this would hurt more than help.

Fair! What I don't know about this stuff is a lot. I'd actually like to see an economist break down what they think is the best way to approach this.

That would have a substantial cooling effect on the housing market as well. (I don't think that's a good thing, but some may.)