I imagine anyone with goals like his is at least somewhat insane to begin with, and (assuming we're talking about the MCU) it's not like it was really any better in the comics where a large part of his motivation was him wanting to impress Lady Death (which I don't think she was).
There is a reason they hammered home the title of "Mad Titan". He was so consumed by his goal, and the method that was previously his only option, that not once did he consider an alternative, even when granted nigh-omnipotence.
