Crypto currency is considered property by the United States Federal Government. Taking or destroying someone else's property is a criminal act.
I am well aware that forking to remove coins can and has been done, but this does not make it legal or morally right.
It is considered "property" only in a very limited way - for tax purposes. That does not mean that you could maintain a claim for conversion or theft if your coins were blacklisted.
If someone broke into your wallet and transferred your XPY, **that** would be conversion. if you sell your XPY for a loss or profit, the IRS will require you to recognize the sale as income or loss. All true.
Blacklisting a coin in a forked blockchain is not the same thing. You still have your wallet, still have your coins. Its just that no one is supporting that old blockchain anymore so the XPY you have in the old wallet becomes worthless.
You would have to somehow argue that U.S. law would protect not just the coins as property, but also your interest in continuing to be able to use the coins on any blockchain. I don't see how this argument could be made.