The actual value being locked up is surely held by the cult, not the owner of the rock? They're the ones who claim to have a bn to spend on a rock after all, the other guy just has a rock. Why can't the cult spend their money on something better than the rock in the first place?

In actuality it's not a rock of course. For a founder of a company the situation is more like you've spent most of your life building something you believe in and suddenly you have to sell it because a group of strangers believe that your thing is worth more money than you've ever seen in your life, and the government wants taxes based on that belief. That seems fundamentally unfair and wrong at least to me.

What is the locked up value of the rock? I like it because it reminds me of my grandfather, and the cult that will buy it will lock it in their storage room.

My point is: With a wealth tax, anyone with money can take anything they want from anyone without money, even if the person without money doesn't value something in the same way that the person with money does.

This is a contrived example that you've twisted yourself in knots to try and justify. There isn't a person on this planet that wouldn't sell an heirloom for $1 Billion unless the heirloom was actually worth ballpark $1 Billion.

The people that wouldn't sell it for a $1 Billion are the people that would give it a way for free, ie: those that have little value for money.

No it's really not. It's an illustrative example of how a wealth tax would (fail to) work. The issue at the core is that items only have value while they are exchanged. Fiat is the only thing with the characteristic of persistent value. So trying to tax standing wealth is fraught because wealth doesn't actually exist in that form.

Then simply don't tax fixed assets. Sure, sure, then people will simply avoid taxes by converting cash and other assets into properties that are not directly taxable, but that's just how these cat-and-mouse games go.

That's what you should be doing because the government should be extracting taxes on the exchange of fiat for for assets and then back to fiat. That's how things already work in fact. People are just angry that other people find value in e.g. Elon Musk and Jeff Bezos when they otherwise don't and want to tax away their entire existence because justice. The alleged problem is those people still have billions even after paying taxes on the acquisition of assets. I'm all for fixing tax loopholes so people can't hide money and avoid existing taxes. How about starting there and actually taxing the tangible before trying to tax the intangible? Companies can and in fact are supposed to grow in value. If the company you own becomes super valuable, you win. If we are unhappy how valuable some companies can become, then you need to cap that and actually break the companies up or progressively more heavily tax profits (which are tangible) such that the company can only become so valuable to investors/owners after which it ceases to provide any additional value because it makes too much money. But since everyone hates Bezos while happily paying for their yearly prime membership, that won't happen. And indeed, Amazon doesn't make incredible amounts of money, it's just ubiquitous and provides a lot of utility which is what makes it valuable. Bezos fought investors for years and years pushing his narrative and strategy of minimizing short term profits to build a company that people literally can't live without and it worked. Crazy. Maybe the government should just buy Amazon...