I guess that would depend on your definition. My body was altered by scientists. I'd like to think I still count as human, though. It didn't change who I am.

[ Because in his mind, the alternative is something like the Chitauri, cold and alien. As far as he's concerned, anyone with a metaphorical heart is human enough, whether they're green or from space or have fantastical powers. Steve sees all of them as equals. ]

Those doors are definitely something, though, and we should probably figure out a containment plan before we keep trying to bust through them in case there's something dangerous on the other side or in case there's no air.