Captain America: Background and actions
What kind of man was Steve Rogers, to fight for America with his background?
In the original comics, he was Irish from the Lower East Side. This means he was probably Irish Catholic from the tenements, which meant he was considered by most Americans with power (maybe) one step above dirt.
On the other hand, he was a tall, blond, blue-eyed man, the Nazi ideal. The Catholic church coexisted with the Nazis without severe discrimination. Many Irish were allied with the Nazis.
He grew up in a multicultural multiracial neighborhood and would have known many people that the Nazis considered less, but he would not have been one of the people they considered less due to their genetics.
So what kind of man could look out, see the horrors that are being done to other people, and choose to ally with the people who treated him and many others like dirt instead of the ones who would treat him extremely well but commit atrocities against others, and continue to do so over the course of an entire war?
And for a laundry list of references related to this...