I've always liked the Gomer Pyle episode where Gomer is in the camp contest to get to sing in Washington, and Sgt. Hacker brings in a "ringer," an opera singer and voice coach, to compete with Pyle. They run into each other, and the new guy sees promise in Pyle's voice and begins teaching him. Hacker forbids him from helping Pyle, and Hacker and Sgt. Carter both try to sabotage the other guy's singer. The contest comes up, both Marines sing beautifully, and the officer making the decision finally flips a coin to decide that Pyle will represent the camp. Pyle immediately protests that he doesn't deserve to go, because he wouldn't be in the running unless the other fellow had taught him so much.

The plot does have one little flaw: after Gomer says his piece, the officer tells the coach that he can get an assignment coaching the Marine Corps Glee Club. Overall I think the episode does an outstanding job of showing people doing the right thing without really expecting immediate rewards, and presenting the whole thing in good humor without heavy-handed preaching.

Are there other shows that had episodes where they showed people quietly and humorously doing the right thing?

Another Gomer episode. I like the one where Andy, Barney, and Gomer take the boys camping. Barney and Gomer end up getting lost and when Andy tracks them down Gomer laughs about the joke being on Barney for all his "pioneering talk" when the boys find out. Andy smiles but explains "the laugh will be on Barney, but I'm afraid it would be the kinda laugh that will hurt him pretty bad.I'd hate to see that, wouldn't you?" Gomer says "Yeah" and "After all, he just came up here to help." Andy got the point across by just telling the truth.

I also like TDVDS where Rob spots a couple running away right after a jewelry store robbery. Laura doesn't want him to report it to the police,and when he does Ritchie's friends say that Rob is a fink. Rob explains that it isn't like with kids doing a little thing, because "when people get bigger, the things they do wrong get bigger. And if you see that, or if somebody hurts somebody, you have to tell."

I know both of these are explaining and not just doing just the right thing, but it isn't preaching. It's just true.

There aren't many since TV is mostly heavy-handed liberal propaganda. One I can think of is an episode of The Brady Bunch where a 10 year-old Jan finds a old picture of a relative of hers when the relative was Jan's age. The relative looks exactly like Jan at 10 and is now probably well in her 50's. She's coming to visit the Brady's and she and Jan have never met, so Jan is very excited to see what she's probably going to look like when she's older. It turns out that the woman is pretty unattractive and Jan is crushed. Then you see that the woman has had an interesting life and isn't obsessed with her looks, or lack thereof. It's done in a somewhat over the top way but it''s still pretty unique for a sitcom.