An unrealized capital gain is an increase in the value of stocks that have not been sold. I am in favor of progressive taxes, but a tax on unrealized capital gains does not seem right. Biden has proposed such a tax, which would initially affect only the wealthiest Americans. The only argument that I can think of in its favor is if stock certificates were used to pay for things, which I have never heard of being done.

Imagine this scenario. In order to pay for a tax on unrealized gains, a person sells a portion of their stock, which increases their tax, because there is now a higher tax on realized capital gains. What a mess!