It's coming anyway and there is no way to stop it, because it's within the realm of politics and not the protocol. Grey markets will of course exist. But it's different from cash, because cash is more fungible, it has no recorded history of transactions. With Bitcoin, coins used in a grey market (e.g. with a coinjoin history) may be difficult / costly to move to the white market, which may result in a split of the UTXO set into a 'white set' and a 'grey set'. Such a split may make the grey markets less efficient due to the lack of division of labour and legal protections.