http://www.laweekly.com/arts/darkest-sitcom-episodes-of-all-time-all-in-the-family-diffrent-strokes-roseanne-8118550

During the ’80s and early ’90s, most long-running network sitcoms at some point decided to go for gravitas and veer into mature themes including sexual abuse, discrimination, depression, hate crimes, murder, molestation and the systemic disenfranchisement of people. The trend began in the 1970s with the rise of Norman Lear’s TV empire (All in the Family, The Jeffersons, Sanford and Son), as his characters regularly tackled tough social issues through the format of 22-minute primetime TV.

By the ’80s and because of Lear's success, this idea of trying to address difficult, touchy issues via mainstream comedy got — more often than not — bastardized into the “very special episode” format, where writers would traverse dark territory more for the sake of sensationalism than to really take a nuanced look at an issue. Throughout the ’80s and ’90s, these dark episodes were usually exploitation fare, but some programs — Designing Women, The Golden Girls, Roseanne — ventured into serious-issue terrain without undermining or trivializing whatever the issue was. (Except, of course, for the Designing Women episode where they all shame a sex worker, which hasn't aged very well.)

By the late ’90s, nihilism in three-camera sitcoms had taken over (thanks, Seinfeld), and with a few exceptions, there's been much less space for politics or social issues on mainstream scripted sitcoms ever since. So here are the most memorable — not necessarily the “best” or the most admirable — episodes where sitcoms got dark (http://www.laweekly.com/arts/darkest-sitcom-episodes-of-all-time-all-in-the-family-diffrent-strokes-roseanne-8118550/2).

Interesting.
Yes I noticed that decades ago TV shows tried harder to incorporate the actual things that happen in life such as robberies, murders or attempted murders, beatings, fights, etc. In a way it seemed some of the shows were acting as "public service messages" to alert people to what was then a social awakening to the fact that violence and domestic abuse and child mistreatment (etc) was more rampant in average people's lives than had been recognized by law and and society itself. ANd of course, a part of it was because it made good sensational dramatic TV.
I was not able to see the entire article using the computer I was using, so I don't know all the shows that were mentioned in that "Top 10" but
there were a few dark episodes on "Different Strokes" other than the kidnapping episode. There was one in which Arnold and Dudley found themselves in the home of a child molester. Another episode showed a scene in which Dudley's father promised him to quit smoking but when he left the room, he just lit up and started smoking. That scene was presented in a haunting way.

All in The Family of course had the attempted rape of Edith but years before that one there was an episode in which Gloria came home and had to reveal to her family that someone attempted to sexually assault her and when the family talked with a lawyer , he told them that the victim would get the worst of it in a courtroom trying to prove the attacker did what he did.
The family decided not to pursue the case. Gloria had to live with the thought of the attack.
Also there was that AITF episode which ends with someone getting blown up in his car.

When I was a kid I thought that "Lassie" had a very dark episode in which Corey Stewart was practically killed off the series by being injured in a fire and then never appearing again in a "Lassie' episode.

Holy moly, Diff'rent Strokes had some creepy episodes!
I remember also one with someone selling drugs in school and threatened the kids.

Also Family Ties had some dark moments: the uncle (played by Tom Hanks!) alcoholic and slapping Alex, Alex taking drugs to study better, or also the suicide hotline.

What weirded me out about the "Bicycle Man" episode was how Arnold and Dudley kept trying to make jokes, as Mr. Horton is literally plotting his next move. The laugh track was even worse. Reminded me of how some of the Miller-Boyett sitcoms would try to incorporate comic relief scenes, and they were just terrible.

HORTON: Hey, let's have some wine and then I'll take my shirt off...
ARNOLD: Whatchutalkinbout pedophile?!
(audience cracks up)

Diff'rent Strokes is probably the only show I know of where the kids were constantly in trouble on and off screen.

About that "Fresh Prince" episode where Will gets shot, I simply can't like the scene where Will guilts Carlton into not using a gun. They made it sound like everybody who owned a gun was a criminal.