I think the fact the price of the stocks going down as it's being sold implies in itself that most of the value is wholly speculative. And for that aspect of the issue in terms of taxation I think there's better targets for it like closing corporate income tax loopholes (ex. Blizzard-Activision in 2017 basically paid no taxes and was paid in effective tax credits from various govts from state and local to make videogames) which is where I think the real problem lies. I don't think anyone should assume the paper wealth of Bezos or Gates is real until they cash out. And if do they, they wind out losing much of that even without taxation.