<p>Personally, my interpratation is that Steven was just not thinking straight since the scenes with the three diamonds show him how changing his appearance (Yellow), mood altering substances (Blue) nor self-harm/taking it out on others (White) will help him deal with his problem. It shows how it won't be easy for him to break cycle of abuse that started with White, went to Pink & got passed to him.
</p><p>Spinel ironically throws his own advice back at him "to change", showing once again how this series has portrayed him as so good at helping others but the trauma he's faced makes all his resentments come back to haunt him just when the diamonds lost theirs makes him the one who needed help all along in a way.
</p><p>At the end of the day, I think Steven didn't mean to do what he did & was just traumatised but he does need to master his powers before he becomes no better than most of the characters who tormented him were.
</p>