David and Mark's abusive mother accounts for some of the most terrifyingly bad "serious moments on a sitcom" scenes I can think of. Awful, awful acting. (And how many other sitcoms did the same thing. Remember Will Smith's dad played by Ben Vereen?) This describes many of the "villain" characters that would pop up on the show: cartoon characters who would make the horrible mistake of pissing one or all of the Conners off so oooooooh boy are they gonna get it now. I mean, Mark ends up getting along with Dan because Mark beats up Becky's boss, a ludicrous bit of plotting that would result in jail time in real life. Wasn't that in that season?
Errmm....no, I think that toaster joke would fly today just fine, and back then too. People complained in the 90s that sitcoms were nothing more than half hour long volleys of vicious insults.
Roseanne and Jackie's dad is no doubt a reference to the abuse Roseanne suffered herself as a kid. Which has probably screwed her up to this very day.