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The key to Saved by the Bell (I'm talking about the high school years, not college or junior high) is what its narrative structure necessarily entails - the way the subjectivity of our consciousness can stretch and distort the way we process reality. The show is about Zack's subjective consciousness - the way he edits and exaggerates events and people in his mind.
For example, the Belding relationship. No high schooler has a relationship with their principal like Zack and Belding. By stepping out of the narrative and acknowledging the subjectivity and narrator's lack of reliability, we realize that the Belding relation is less about a friendly, bumbling principal and more about Zack's obsession with power figures.
Other relationships can be changed as well. Zack was probably a complete hose to Screech, but through his subjective lens his treatment becomes more charitable to audience. The way there are 6 students, plus a handful of minor characters, is Zack's subjective editing. He is probably only notable at his high school for being a dick to a large number of people - he exaggerates his popularity, appearance and achievements.
However, once we accept that Zack's subjective perception is at the core of the show, the most important characters become Slater and Lisa - because they are minorities and they come off as a total cad and a heartless bitch, respectively. While they might actually be that way, because these two people - who are presented as totally obnoxious - occupy such a large part of Zack's consciousness can only lead us to the conclusion that Zack Morris is a racist. A normal person would probably ignore them, but Zack is a racist and enjoys the kind of perverse mental tingle he gets from believing that these minorities are annoying.
This conclusion also helps answer the question - Why do people think Lisa is fashionable? It is because we are not allowed to see the actual Lisa - who might be wearing perfectly normal clothes, rather than the terribly odd stuff she is wearing. We only see Lisa and her sense of style after it has been exaggerated and distorted by Zack's polluted, bigoted, racist mind.
An open question is whether the show itself was a sly satire of American racism or an example subtle racist propaganda.
