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The problem with that scenario: if you ban Monero by name, and do not ban its attributes, you'll end up with dozens of forked coins to take Monero's place--Monero doesn't break any laws, so laws would have to be made (and then designed around) to make Monero illegal, and the more specific the law, the more likely you'll just get a whack-a-mole scenario similar to designer drugs. Plus, you seem to miss that US law isn't world law just yet(China and Russia might embrace Monero or vice versa if countries want to go that route) and it's still impossible to keep people from downloading wallets or creating games that don't use Monero as game currency, but certainly give you the option to deposit XMR, move to a country where it's legal and then spend as you see fit (CK plug).