the world ruled under one person is ideal, but such a thing cannot be achieved without a great conqueror like alexander the great, julius caesar, napoleon bonaparte, or adolf hitler. war is the only way to create such unification. but most powerful countries in the world do anything to avoid war.... so such a conqueror probably wouldn't obtain power.
as for loyalty, i think what you are trying to suggest is an absolute democracy with no leader... such a thing would be highly ineffective on a large scale unless there was a secure form of wide-spread communication, and the internet just isn't that reliable yet.
as for terrorists, hate DOES beget hate, but put yourself in their shoes. they have no country to support their views, they have no freedom to live the way they see fit, they want change and love isn't going to win them a home. America once rebeled against the world (mostly the british and native americans) for our freedom, is it so wrong that these people rebel against the world for theirs? i'm not advocating that they should win, i hope they lose and i get to keep my way of life, but i am not close-minded enough to say they are foolish.