West Wing is one of my absolute favorite shows. Aaron Sorkin is one of the greatest writers in entertainment (in my opinion). I've never seen this clip referenced when defending Liberalism, but I think it makes a great argument.
The idea of an "Intolerant Left" also makes no sense to me. The only rationality I can think of is my own. I AM intolerant of a government using legislation to discriminate. I am intolerant of people who are intolerant. And I think that's how most liberals/progressives/democrats/leftists feel.
(P.S. I have not fact-checked all of the statements in this video, so if The Great Sorkin made any mistakes, let me know)