As a less famous superhero, the terrible things that Iron Fist does are generally less well known. This is arguably the only way the man is still considered a superhero, as almost every single comic involving him contains at least one moment that seems legitimately awful.
This largely comes from two factors; that Iron Fist is 99% likely to be mind controlled in any given comic, and also that even when not mind controlled, the dude has some pretty questionable morals.
For example, while a mind controlled Iron Fist almost routinely fights his friends and teammates, a totally lucid Iron Fist is more than willing to beat up a totally innocent child, should it help him achieve his goals.
Be it down to his intense and terrifying childhood, the terrible things that happened in his adulthood, or just that he never had a particularly strong moral compass to begin with, Iron Fist is as likely to betray or beat up those close to him as he is to actually help them. While this does make for one of the more interesting superhero dynamics within Marvel, this is because you're left unsure if you should consider him a hero at all.