Of course, a state can tax billionaires. They can apparently even tax individuals for deciding to leave a state with unfavorable tax policies like California. If they could, I don't doubt that politicians in California would like to be able to tax people who just THINK about living in California.

While the state CAN tax billionaires, state legislators CANNOT predict how billionaires will change their circumstances in pursuit of a more favorable tax climate. Even paying an exit tax may be more desirable then continuing to live in a high-tax environment.

One thing is for sure, billionaires will make those decisions based on logic and math and not emotions. If they decide to leave, you write "Good riddance, and don’t let the door hit you on the way out". But billionaires don't become billionaires on capital gains alone. They generally produce and employ large numbers of people potentially encompassing multiple companies.

If the billionaire relocates the companies, some if not the majority of those employees may also leave the state taking their tax revenue with them. I think the laws are too young to know that full impact. It's awful cavalier of you to simply dismiss the potential immediate and long-term state AND local tax implications of that migration because you have a hatred of billionaires.

I doubt California was happy to see SpaceX Headquarters (and its well-paid employees) move to Texas. In fact, reporting indicates at least 89 companies with 100 employees or more have left California in pursuit of more business-friendly states since 2020.

Who cares if people might've lost their jobs because they were unable to move and the state and local governments lost part of their tax base. California sure stuck it to those rich folks.