I also get all kinds of annoyed at the ancestry question because while I know the exact place in Germany where my ancestors came from, it was in the early 1700s, before the Revolution. I have no affinity for Germany and don’t consider myself German-American. I’ll leave that question blank.
I have plenty of family who showed up before the revolution (Dutch and German), and while I think it's cool and their place of origin is interesting, and would readily tell people where my ancestors came from (Scotland, Wales and Ireland in addition to the above), I agree Americans are WEIRD about being obsessed with their ethnic origins, man. People in other countries are like, "Okay, you're American. You're not REALLY Irish."
I have the opposite problem. Of course the locals make fun of the Americans who are all "I'm Norwegian! My great-great-great-grandparents moved to the US from Lillegård, and I'm here to visit my homeland!" (They even made a reality TV show out of it), but they also assume we're all like that, so they often ask me where my family is from. "Where is your family from?" "The US." "No, where did they come to the US from?" At that point I explain that my first ancestors moved there in 1682 from England, but since it was so long ago, there are dozens of family lines that moved over at various times since, so of the ones we know of (my parents are both genealogy buffs) I'm mostly English, Scottish, Irish, Welsh, and German, with a tiny bit of French and Swiss.
For the record, I am in no way suggesting that the 2020 census is going to be used for nefarious reasons... but I read this article today and it made me think of this thread.
This is the perfect example of how we can learn from history. There is a REASON we don’t ask citizenship questions on the census. There is a REASON why people are afraid to systematically provide this information to the government. Regardless of how the information will be used, it is unreasonable to expect people to be ok with this given the historical context, especially in conjunction with the current policy climate on immigration.
I am not sure I necessarily think the data will be mishandled to personally identify people (though that is definitely possible), but there is a very very high likelihood that if Trump wins the presidency again in 2020 we will see citizen-only counts used to determine federal funding allocations, Congressional redistricting, and other government functions that use census data. Those are supposed to be determined based on population, not based on population of citizens.