>Many countries use census data to target (or even round up and murder) specific groups of people by religion, ethnicity, etc.
You were asked to back up this claim but haven't cited an example of any country currently "using census data" to "round up and murder" people.
Is China currently using census data to do horrible things? Are other countries? Maybe. I have no idea. I wouldn't be all that surprised TBH. You may be correct for all I know.
But that's not the point... The point is that you made a very specific claim and you still haven't provided any specific examples or evidence.