Universal Democracy: Should everyone have a say?

With the advances in technology and the "shrinking" of the world in the last century, people are much involved with each other on an international scale. Given this, would a single democracy that would rule the whole world be feasible? Would it be better for all humanity to vote and weigh in on all the major issues, and have a direct system? With the technology of the internet available to us, it seems that this form of total democracy could work, but is it the correct thing to do? Are all the citizens of the world responsible enough to have a say in the lives of everyone else?

Your thoughts please...