The very beginnings of marvel were founded on misunderstood outcasts and heroes that people don't understand. It's a much more minority friendly set-up. People hate and fear the X-men, the Hulk, the thing is judged on his appearance, and Spider-man is hated by the media when he's just trying to do his own thing. That's already a strong parallel to how minorities are often treated without even having to bring in minorities. When you do bring them in, they just kinda fit right in.