Nothing, actually, but he was afraid Onslaught taking the Earth. Everyone was afraid, also heroes, and it's not necessary to express fear, even if you are afraid, especially such beings as Dr. Doom.
Dr. Doom, such evil and then joined the Earth to stop even greater evil.
Why did he even care?
That doesn't mean he was afraid, but probably was, deep inside them, everyone was.
It's not necessary to show fear, if you are afraid. He joined the Earth to stop Onslaught, at least, he obviously cared. Something bothered him if he joined, something about Onslaught.
It doesnt' matter if he went toe-to-toe aganist Beyonder, he dind't go against Onslaught. And he had plan to take Beyodner powers.
So, he wasn't careless. And I said, it's not necessary he was afraid, but if he joined in goal to stop the Onslaught, that showed he did care for something, maybe afraid of Onslaught taking over the Earth.
I agree.
But I think there is always something, that you are afraid, maybe even for Dr. Doom.
Maybe not power or some threat that he would fear or something like that, but in some other way. There is always almost something.
I know Dr. Doom, but not that good enough. Was he afraid of anything through comic books?
There must be something?.