Throughout this all, Doctor Doom is reserved, almost reactionary. He doesn't go looking for fights, but finishes them utterly once they start. He doesn't commit genocide against other alien invaders, just wrecks their ability to make war. He doesn’t go out looking for a fight with The Celestials, he just stops them from interfering in the affairs of lesser civilizations because they interfered with his. He gains the Inifinity Gems because he's confident that he can and should wield this power. While I haven't read any of the “Infinity Gauntlet” that wasn't written by Brian Clevinger, I'm pretty sure there was a lot of fucking hand-wringing over what to do with the Infinity Gems once Thanos was defeated. A lot of “that's too much responsibility for one man”s being thrown around. While Doctor Doom doesn't doubt the morality of his actions, once he can surpass his petty desires to rule the world, avenge himself on Reed Richards, and save his mother's soul, his moral compass points as well as any superhero's that doesn't doubt itself and eagerly agrees to ignore The Prime Directive if someone else does first.
It's strange that Doctor Doom's actions in this story still aren't heroic; they're responsible. He doesn't have that moral myopia that only lets him hit the guy in front of him. He'd rather the job be done definitively than to keep bloodshed at a minimum. The exception is that he doesn't concern himself with the massive consequences of fighting the most powerful beings in the universe because he is right and they are wrong. Indeed, that kind of moral myopia isn't foreign to Doom, it's actually his normal level of petty elimination of people who oppose him. He will change the status quo of existence itself because it inconveniences him. That the consequences destroy Earth are no matter; he uses the last of his power to give the Earth a glorious rebirth. Of course, Doom himself is given a rebirth as a simple human, so much the better to begin his quest anew.
Doom must strive. Doom must oppose. It's only in adversity that Doctor Doom finds his calling. It's only by punching so far above his weight class that he can find the challenges that a genius—nay, a man—of his caliber requires. The central point of his character isn't to protect others or even to take his petty vengeances, it is to seek, to strive, to find, and not to yield (Yes, Tennyson). It’s the same unquenchable fire that drives heroes, but its direction is totally inward, pushing Doom to test and prove himself. Doom must be the best, he must be worthy of his own image.