During the 1980s, the buzzword was "family values," which meant that only people who had heterosexual nuclear families had value. We heard again and again that the only life worth living involved husbands and wives raising horny teenager and wisecracking preteens. That's why Married...with Childrenwas such a big hit, immersed in a pool of Family Ties, Family Matters, Growing Pains, The Wonder Years, and The Cosby Show. 
After a season and a half, Harper left in the midst of a salary dispute -- and proved not indispensible. Her character was killed, Aunt Sandy (Sandy Duncan) moved in, and the renamed series got top ratings for another three years.
As is common in nuclear family sitcoms, the kids soon took over. The twins usually had episodes involving cheating, bullies, staying out past curfew, friends (notably Andre Gower), and the "discovery of girls." By the last season, they were as heterosexually active as David.
.Especially in later seasons, when he toned up. Here's what he looks like after Hogan.
Jason Bateman was mostly ignored, too -- there are no shirtless teen idol pix of him anywhere. But his David got most of the serious episodes (premarital sex, drunk driving, gambling), and he had ample time for buddy-bonding, particularly with the gay-coded teen-operator Rich (Tom Hodges).
They didn't specify how he contracted the disease, but as this was the first sitcom AIDS episode where everyone didn't yell "Blood transfusion!" over and over, the silence was more than enough to tell us that David's friend was gay.
Most of the cast members are gay allies. Jason Bateman has played gay characters many times. Jeremy Licht and his wife Kimberly are vocal supporters of gay rights; 2012 he participated in Brice Beckham's CCOKC video (Child Celebrities Opposing Kirk Cameron).
There's a Jason Bateman story on Gay Celebrity Dating Stories.
See also: Danny Ponce