It was halfway decent and acceptable until they decided to make Urkel the main character and have entire episodes built around his WAAAACKY inventions.

I dunno... Did they ever time travel or do a "body switching" episode?

http://television.aol.com/episode/father-time/family-matters/13777

There was also about a dozen episodes featuring Urkel's "transformation chamber", which apparently turned people into different family members, suave lady's men, and Bruce Lee.

I just don't understand how they can go from a sitcom about an African-American family to science-fiction. It's like the gradual acceptance of fascism.

As far as I know, this is what happened: It started out as a sitcom about middle-class working African Americans, perhaps as a response/alternative to shows about rich blacks like "The Jeffersons" and "The Cosby Show". Then they brought in Jaleel White for a single episode, 'hilarity' ensued, and audiences demanded more Urkel. Suddenly the rest of the series revolved around him and you could buy a talking Urkel doll with a ripcord. The end.

And Urkel-O's cereal!