Prior to Fox, there were "conservatives" on TV, but they were all cartoonish people designed to play villain so the liberal savior could come in and rescue the show.
CNN, for instance, would ask conservatives to be on their shows and talk about how much they love David Duke. Then 3 liberals could pounce on them and look like the good guy.
Fox didn't just put conservatives on the air. It put conservatives on the air who weren't foaming at the mouth attack dogs. Imagine if the ONLY left-wingers you saw on tv were James Carville and Michael Moore. That's what TV was like before Fox.
My recollection is that both George Will and Charles Krauthammer were on the air before FoxNews, and I'd hardly call them "cartoonish." WFB had Firing Line for only like, 20 years. The real problem--other than Firing Line--always was that the conservative was completely outnumbered and often shouted down or ridiculed. PBS marginalized Firing Line by showing it late in the evening, or even after midnight in many markets. And it was only ONE conservative star in a very liberal galaxy of programs.
The big difference on FoxNews is that all commentators are treated with respect. (Even some, such as Juan Williams, who really deserve none.)