Can we ever develop ourselves into, or create, a truly peaceful and unified species? And could there be peaceful, unified, civilized species in the stars?

(I'm not going to get into the inevitable pushback around the idea of radically defining the human genome or alternately creating an AI successor species), but is it possible to have a populous species either on Earth or of alien origin that is free of internal violence and conflict by using some combination of AI/programming, genetic modification, drugs, and/or education? Or would that species inevitably either stagnate or be crushed by natural selection and the realities of finite resources per star system? To quote an old sci-fi author:

The optimist proclaims that we live in the best of all possible worlds; and the pessimist fears this is true. -J.B. Cabell