citizens are generally taxed on worldwide income and expatriation carries its own tax consequences.
So the national question is not whether wealthy people would all leave the United States. Most would not. The better question is how much income would disappear from the tax base before it ever appeared on a return.
The surtax and the wealth tax
That brings the surtax into comparison with a wealth tax.
The Massachusetts surtax taxes flow. It applies when income appears. A wealth tax taxes stock. It asks what a person is worth.
The difference is simple to state and difficult to administer.
An income surtax is blunt but collectible. The government already has a tax system built around income: wages, bonuses, capital gains, business income, pass-through income, interest, dividends, and taxable distributions. There are avoidance strategies, but the basic measurement system exists.
A wealth tax tries to reach what the income tax misses: the fortune itself. That is why it is attractive to its supporters. The richest Americans often do not live mainly on salaries. They hold appreciating assets. They borrow against them. They can defer capital gains for years, sometimes until death. A surtax on annual income may miss a billionaire in a low-realization year. A wealth tax would not.
In theory, that is more direct.
In practice, it is much harder.
Publicly traded stock is easy to value. Cash is easy to value. Treasury bonds are easy to value. But large fortunes are rarely so tidy. They include private companies, real estate partnerships, private-equity interests, hedge fund stakes, intellectual property, art, collectibles, trusts, family limited partnerships, restricted shares, and other assets with no daily market price.
A wealth tax would require an annual valuation system for the rich. Taxpayers would argue for discounts. The government would argue for higher values. Appraisers, accountants, and lawyers would become central figures in the tax system. Every major fortune could become a recurring audit.
That does not make a wealth tax impossible. It does make it harder to enforce than a surtax.
It also makes it more legally vulnerable. A federal income surtax fits comfortably within the existing income-tax structure. A federal wealth tax would almost certainly face a constitutional challenge over whether it is a “direct tax” that must be apportioned among the states. Supporters have arguments. Opponents have arguments. The Supreme Court would likely be asked to decide.
For a working government, that matters. A tax that is theoretically elegant but administratively fragile may raise less than promised. A tax that is less complete but easier to collect may do more in the real world.
What Massachusetts proves — and what it does not
Massachusetts has proved that a millionaire’s surtax can raise large sums of money. It has not proved that high-income people never respond to taxes. It has not proved that there is no migration cost. It has not proved that revenue will be equally strong every year.