Unless we are talking about dividends (I assume not), capital gains are not income until they are realized (something is sold), but as I read your replies, you shifted to talking about seizing capital. And then you shifted back to taxing income. Seizing capital is a wealth tax. You might as well call it that so that you don't confuse people. You may think of both categories as the same thing, but they are two different things which must be dealt with in different ways.
Property taxes on houses are wealth taxes, so you would be using a similar model for stock assets. This isn't a new idea but implementation has been found to be difficult, house values are easier to estimate than stock values, which are much more volatile and depend on a lot of intangible factors. The main purpose of stock markets is to estimate the value of public stocks, but it's far from perfect. Private company values are even harder to estimate. This will be an uphill battle for advocates of a wealth tax.
