GenXer here. Arthur was after my time, so I sat down to watch the episode in question here:
https://www.youtube.com/watch?v=GlIJuuEDyB0Jesus H. Christ, no wonder you millennials are so fucked up. The parents never addressed Arthur's reasons for using violence. DW was never punished for blatantly violating Arthur's personal property, even when she was told not to. DW was also never called out on her faked pain symptoms. Being peer pressured into punching someone is NOT the same as emotionally striking out at someone who wronged you. Last, the bully never got punished for punching Arthur. In some ways, you can say that he got rewarded for doing so instead.
Growing up watching "edutainment" shows like this with such broken Aesops would turn anyone into a raging SJW. Even the old He-Man & GI-Joe PSA's were better at teaching life lessons. And they had swords & explosions!