I'd go with no. And very simply because of human nature. Altough Platon said that humans are social animals, they are also deeply selfish. Never ALL humans would agree. Specially cuz being so selfish, one's answer, vision, solution would ALWAYS be the correct one. And everyone, or at least, the great majority thinks like that, wants to be right. There is fanatism, there is crazy people. The great "mark", the great "symbol" for human kind is it's diversity. There'll be no earth without diversity. Think about how to make the world one? Witch culture choose? Witch language? Currency? Flag? Anthem? Every country, every culture, every religion proclaims to be the best one...
See why problably there'll never be unity?