Rockwing acted like Petalcloud was invisible, she runs away but gives him Frostfire, Rockwing raises Frostfire to be like he is now, and then you have two pegasi who are dangerous. Years before, the over-stallions treat Nightflame like he’s some kind of object meant to do what they say. They treat him good, but different. And only for his starfire. So he feels left out. Hollyblaze, the pegasus who’s apparently supposed to be his only true friend, doesn’t seem to respect him and she doesn’t trust him with the starfire. Hollyblaze dies and she blames him, and then the herds shun him when he has his starfire but doesn’t know how to use it. So he flees Anok, goes through a bunch of horrific nightmares, and much more.
Rockwing, the evil ancient over-stallions, and Hollyblaze are all the reasons the seemingly main antagonists are villains in the first place. They’re the reasons that Nightwing, Petalcloud and Frostfire are the way they are.
This is how I like to think about it. It helps me feel more sad for them instead of just not liking them.