Based on this post, apparently citizenship is also voluntary. You might say that giving up citizenship is difficult and expensive, but you should talk to someone who has gone through a divorce.
I would also counter that citizenship also almost always necessitates an emotional element. Citizenship is a primary part of many people's identity, and identity is the most emotionally charged thing of all.
I mean sure, but on the other hand WTF? I understand not sharing the emotions regarding the country, patriotism, the 4th of July, the standing for the pledge from school years onward etc. but despite your freedom from the effects of all this it should probably cross your mind that not everyone else is free in the same way.
I would also counter that citizenship also almost always necessitates an emotional element. Citizenship is a primary part of many people's identity, and identity is the most emotionally charged thing of all.