A wealth tax on unrealized gains has been proposed as a means of addressing wealth inequality and funding public programs. However, there are several risks and potential drawbacks associated with implementing such a tax, including:

1. Liquidity Issues: Unrealized gains are not yet cash. Someone might own a lot of wealth on paper because of the current value of assets like stocks, real estate, or a business, but they might not have much liquid cash to pay a tax on these unrealized gains. This could force individuals to sell their assets, which could cause a variety of market disruptions.
2. Valuation Difficulties: It can be difficult to accurately assess the value of certain types of assets. For example, private businesses, art collections, and real estate can be challenging to appraise accurately. This could result in inaccurate tax calculations and disputes.
3. Disincentive to Invest: If investors know they will be taxed on unrealized gains, they may be less likely to make risky investments, potentially slowing economic growth. They might also be incentivized to shift their assets to more tax-efficient forms of wealth, which could distort markets.
4. Capital Flight: A wealth tax might encourage the wealthy to move their assets, or even themselves, to jurisdictions with more favorable tax policies. This could result in capital flight from the country implementing the wealth tax.
5. Administrative Complexity: Implementing and administering a wealth tax on unrealized gains would likely be complex and costly. Taxpayers may also face significant compliance burdens.
6. Legal Challenges: Depending on the jurisdiction, there may be legal hurdles to implementing a wealth tax. For example, in the United States, some argue that a wealth tax could be unconstitutional.
7. Potential for Tax Evasion: As with any tax, there is the risk that individuals may find ways to evade a wealth tax on unrealized gains, particularly given the difficulty of accurately valuing certain types of assets.

It’s important to note that these are potential risks, and different policy proposals could include measures to mitigate these risks. The actual impact of a wealth tax on unrealized gains would depend on the specifics of the policy and how it is implemented.