Punching hard objects indiscriminately is a good way to break your hand, that's true. Punching well and not breaking your hands requires training. Most people don't have that training, and hence break their hands when they try.
Punching someone's forehead with a horizontal fist, impacting with only your pinky knuckle with a bent wrist is going to cause one some problems.
Striking properly will cause one less problems. Different schools have different ideas on the best way to do that. I'm a vertical fist, bottom three knuckle guy now. When I did Arnis, I was taught top two knuckles, and a variety of fist orientations, from horizontal to vertical to angled in between.