To all individuals equally? weighed against individual risk?
- generic wealth level
- generic education level
- living in a particular area of the country
- having small children
You could probably find more examples like those if you browse the history of humanity. The point is, you can be targeted over anything, and you can't predict what it will be in advance. The Nazis exterminated members of religious minorities and different sexual orientation, which was somewhat unusual in history. The Soviets killed people with high educational credentials and with lots of wealth. Who knows what the next evil empire will pick as an excuse to murder people?
You can't run a society on the assumption it's doomed and everyone will get massacred. That some particular demographical data will be used to select and murder people is a low-probability hypothetical. That it is useful for managing a country right now is a fact. I get one not wanting to be oversharing about oneself, but I don't think that a remote possibility that a piece of demographic data will be used for evil purposes is grounds for ditching censuses altogether. This is not something we should be paranoid about.
Finding yourself questioned, monitored, surveilled, on any kind of "list" (no-fly, hollywood-black) or at any kind of increased risk or action by any actor, state or otherwise, is a risk to be weighed against whatever gain you might make from accurate stats.
> Who knows what the next evil empire will pick as an excuse to murder people?
An argument for giving up less discriminating information in general.
> You can't run a society on the assumption it's doomed and everyone will get massacred.
Much of the US constitution seems centered on protecting the people from an overly powerful government, and restricting said power. Make this sentence less hyperbolic, and you can run a society based on certain assumptions of corruption and abuse.