but they did nothing when she would.

Yeah, that was the biggest bullshit of the show.

Arthur was wrong to hit her....but that seems to be the only lesson they were going for in the episode.

The people who wrote the episode seem to have no clue about parenting.

A big thing with kids is them feeling like they have no control in their lives, and that absolutely causes them to act out sometimes.

That episode only reinforced that. DW never faced a single consequence. Their parents never tried to correct her behavior and teach her to respect her brother's boundaries. And in the end acted like she was the sole victim. They went with a "little kids will be little kids" attitude. No. Parent. Enforce boundaries. Explain to kids that two people can be wrong in the same situation (ie touching another person's belongings without their permission is wrong, but so is acting out violently because of it).

Honestly, I think Arthur sucks as a kid's show when it comes to teaching life lessons.

PBS has done much better with other shows, past and even present.