Carlin also remarked, "Inside every cynical person, there is a disappointed idealist".
Carlin could be an example of the Sliding Scale itself. He developed a squeaky-clean image during his early years. His humor became political in the 1970s. Throughout his career, his humor gradually grew darker as he grew older, culminating in the pitch-black tone of his later, post-9/11 specials (his "American Dream" routine turning out to be a bleak summary of his later years).
UK comedian and political activist Mark Thomas is often accused of being a cynic, because he always assumes the worst of the government and corporations. He insists that he's an idealist — he believes he can change the world for the better and is prepared to try. It's the people he goes after, who "invite evil in for a cup of tea", that are cynical.
Australian comedian Adam Hills is firmly in the idealistic side. Early in his career he decided his joke "The reason I hate Americans; is that they name their children according to virtues they want them to imitate..." worked just as well with the word "love" instead of hate, and in the end, made the whole thing a lot funnier. His act is very uplifting and positive.
Which made the 2008 Christmas Special of Mock the Week hilarious, where he was sat next to Frankie Boyle and Hugh Dennis. That's both ends of the scale at the same table.