For what I've understood of the movie!Ultron rationale, having as goal peace-keeping, he devised what he thought was a better way to do this than the Avengers itself: instead of maintaining peace by fighting the enemy of peace, do it by evolving a new kind of human being (the project that eventually phyzvangrq jvgu gur nppvqragny perngvba bs gur Ivfvba) and then killing all the older ones.
Screw with the fact that there's no continuity between the latter and the former... :/