Is it legal citizens that aren't the right race, or is it legal citizens that were previously foreign nationals?
2. As far as I can see, the position that DHH referred to did not apply to naturalized citizens, but to foreigners. So non-citizens.
3. As far as I know, most countries currently have laws on the books that can result in citizenship being revoked. As an example, countries that don't allow dual citizenship will take your citizenship away if you become citizen of another country. Germany and many other countries will take your citizenship away if you lied on your application and it only comes out later. Terror and treason are also common reasons.
4. Some counties (India for example) will even take your (naturalized) citizenship away if you are out of country long enough.