That's not a plot hole. You'd have to ignore his backstory to consider it one. He was branded as a mad man and exiled by his people because he proposed dispassionately killing half of their population. He wants THAT solution to the problem to be the one that works. Not creating more resources, which his people probably advocated, but the one that got him branded a mad titan. It's his philosophy that he built a cult around, and he gets to prove to everyone and himself that he was right all along. The fact that he tried his solution on various planets and saw those planets improve the quality of life has only emboldened him to try it on a cosmic scale.
His backstory informs his character journey.
Thank you...his whole journey has been about sacrifice. He believes the only way to truly achieve balance is through sacrifice, any other way will eventually fail.