While that be MIGHT be true that you can’t solve a problem unless you know the exact extent of the problem I question how you know the motivations of people gathering this data. Especially since it started well well before the civil rights movement.
When I see bigots doing x,y,and z and people claiming to stop bigots doing x,y I wonder if z is coming later. Specifically do you really think the last census was going to ask about citizenship information to ensure racism would be diminished?