This particular implementation wouldn't actually work. Anyone can send BTC to any address, so it would be easy to poison the well.
You could easily have software that would automatically turn over to the government any coins sent from addresses that are not registered. It's like if you found a briefcase full of money: you'd turn it over to the police (or maybe you wouldn't, but that's what you should do). With software, it could just be automatic.
If you refuse to run software that does this, or you don't turn over coins received from blacklisted sources within some period of time, you get blacklisted.
You could easily have software that would automatically turn over to the government any coins sent from addresses that are not registered. It's like if you found a briefcase full of money: you'd turn it over to the police (or maybe you wouldn't, but that's what you should do). With software, it could just be automatic.
If you refuse to run software that does this, or you don't turn over coins received from blacklisted sources within some period of time, you get blacklisted.