User blog comment:ElectricMayhem/Best Avenger - MCU - Final Round/@comment-24799099-20150726211251/@comment-5795364-20150727145755

He has a choice.

He can choose to kill ultron directly. He can corrupt him. Both of these are perfectly valid and good ways.

Yet he chose one of them for this mission.

And that's because he didn't have an objective for creation. Ultron's objective was: "Bring peace". He could do what the Avengers thought, but instead he thought killing all organic life is easier.