> every citizen votes, and shares responsibility in decision making process
Why? I never consented to be a part of the system, don't agree with it, and in practice can do nothing to change it. Saying I'm responsible for it because I happened to be arbitrarily born with a particular citizenship is meaningless.
> In democratic system...
There is no reason why I, an unrelated individual, should have to ascribe to the ideals espoused by proponents of the system imposed on me without my consent.