You are right, and I guess each guy has its own reasons to be a villain.
Galactus wasn't really a bad guy, he just had his hunger
Apocalypse is like (but not much) Dark Sied. He wants to rule this world and bring an end to Humanity.
Joker is evil incarnated, but he does believe he can break anything,or anyone including Batman, Superman, Flash, etc.
Magneto wants a world ruled by mutants, not because they are powerful but, cuz its their right.
I would like to point out that Magneto is more relatable to leaders in history and today. He was the Fidel Castro of Genosha, and his beliefs are pretty similar to ones living amongst us (So-Called-Jihadis, Democrats, Socialists, Communists, Evangelists, etc). he would do anything to get Mutants in power, just as our leaders sacrificed its people to unknown horrors. He would even use his children, or friends (Polaris) for his own evil purposes/designs. He unlike Doom doesn't even want that power.