1. Kerry knew Cavett was on his side. (Which may be why Kerry did not want to debate O'Neill on other shows).
2. Kerry knew he could lie and get away with it.
Well, at least you agree with me about the favoritism. Cavett was anything but even-handed. As the host, he should have done a better job at controlling the audience.
I don't think any television host today would risk looking supportive of an audience jeering at U.S. servicemen putting their lives on the line.