If a majority stock holder in a company sells all of their stock, the price first the first share sold is likely going to be completely different (and substantially less!) than the last share sold.
Personally my favorite idea for this stuff that I have heard thrown around is to allow people to self value everything. However, that self valuation then becomes a price tag. Let a billionaire's accountants put their own evaluation on their equity in a business. But that becomes a binding offer and some other billionaire could come along and buy them out at that valuation. That creates pricing pressure in both directions, the person is prevented from underpricing their assets due to the threat of another buyer coming in and a person is prevented from overpricing because it increases their taxes. And suddenly all the problems regarding how the government appraises these things disappears.
And that ignores that it trivially enables large-scale exploitation and looting by construction.
Once again, this is simply haggling over price. Name the premium you think is justified and add that into the law.
If the owner is required to invent a fake risk premium then it virtually guarantees that the risk will be mis-priced. Forced rampant mis-pricing is an exploitable arbitrage opportunity of epic proportions. Every quant worth a damn will make a fortune looting this. No serious policy can ignore this defect. It has the additional political downside that no one can ever own anything anymore in a meaningful way, which won’t be popular.
No one takes this idea seriously because anyone with a modicum of finance math background can see that the math doesn’t math. Political ideology doesn’t even figure into it.
For example, imagine we only apply this to people with a net worth over $500B. That's literally only Elon Musk. He has plenty of money to hire his own team of quants to price his assets. We can even be generous with this law and make the purchase price double the valuation. Hell, we can even restrict it to only apply to stock of publicly traded companies so the wealth valuations are highly informed by market pricing. We can just keep adding rules like this until you're out of economic reasons for why a wealth tax and/or this form of valuation can't work. At that point the debate is lost and "we're just haggling over price" because once we apply it to Musk, how can you argue against applying it to Bezos...
This type of forced sale happens all the time with public companies. For example, only like 60% of Twitter shareholders approved the sale to Musk, but the other 40% were forced to go along with it regardless of their preference. If Musk can do that to other people, why should some hypothetically richer person not be able to do it to Musk?
And to repeat myself for a third time, we don't need to haggle over price. If we only want this to apply to billionaires, assets worth $50 million, or whatever, that's fine. If one of the people impacted truly doesn't want to sell, let them set the price as high as makes them feel safe. I'm not going to lose any sleep over taxing the emotional desires of billionaires.
They signed up to that, though. Tagalonpg/dragalong rights are priced into the share price. That's not the same thing.