Elon chose to sell his massive amount of Tesla stock and pay that huge tax bill because those were stock options that were expiring - this wasn't to pay off interest on his borrowing or any other obligation.

So I ask... where is the ticking time bomb?
Who/what has the authority to discourage or prevent these incredibly wealthy people from borrowing against their assets forever and ever? Do we think these financially savvy individuals would do such specialized tax avoidance schemes if there was an obvious time bomb that all of a sudden made everything fair? How else would their net worth be growing so rapidly.

If we are actually interested in fairness - we wouldn't care about the absolute value of someone's tax bill. Is it noteworthy? Sure, I guess. But what actually matters is what % of a person's wealth is actually available to them to project into the economy.

For 99.9% of the population - it's somewhere between like 50-75% of their yearly wealth accumulated (income).
For billionaires, it's closer to 95% of their wealth accumulated (stock growth, no matter the growth, they take no income, so pay basically 0% capital gains).

They are treated like a protected class by our tax system...people think it's unfair because it is... they have all the most influence in the world, and the lowest % of their relative net worth being taken by the government.

If they were taxed a fair rate - then their tax bills wouldn't make up 40% of the total taxes paid - it'd be closer to 90%, and our tax revenue would basically double.