Heros should involve helping people for the good of man kind sort of thing.
Nope, heroes are those who take history-changing action which benefits both them and several others. They'll be called "heroes" by those several others who also benefitted from it. Disgusting devils/monsters by those who lost something (or someone) important because of them.
Besides, nobody does anything "for the good of man" (whatever the definition for that "good" may be). The goal of helping someone will at best involve feeling better about oneself. Which is, ironically, pretty egocentric.
In Skyrim the only sort of hero quest is the main quest. And I honestly cant tell if I am killing the dragons to save man kind or to absorb their souls and become more powerful. Its not like Oblivion where you were closing the oblivion gate to save cities. You never got more powerful from that. In Skyrim you gain power from every dragon kill.
Well, I'm not really playing the hero in Skyrim. Just being someone who defends herself when attacked (and since every enemy attacks to the death, I'm pretty forced to do the same if I don't want to continually run away everywhere). Besides, not all random dragons attack you, and so I leave them alone. For the ones on their lair aka word wall, I even pop up an invisibility potion in order to not disturb them while learning my shout. The only one I have beef with is Alduin after all, since he either has the duty of destroying the world (and thus threatening my cosy little territorium called home and friends), or conquering it with an army of dragons (and during the latter he wants to kill me). So no souls for me if I can avoid it. Dragons are animals too after all. ^^
About Oblivion, well you were at war with an Oblivion plane there. It was you or them. No real choice in the matter. They were invaders after all. And of course you become a hero to the people in the cities and such. I bet you're quite the opposite to the inhabitants of Mehrunes Dagon's Deadlands. But yeah, they're daedra, so why bother? Well, having become Sheogorath, I guess the relationship between you and Mehrunes won't be great, to say the least. Oh yeah, does this make Sheogorath a hero?