As for George Carlin (the actual topic of this thread) he was certainly extremely critical, given to fiery and hyperbolic political speech. But I have no reason to believe he was actually a conspiracy theorist.
I've been a fan of his for almost as long as I can remember, ever since I was a kid in the late 1970s & early '80s, laughing my ass off to The Hair Piece, Toledo Window Box, and FM & AM. I've read his first 4 books (having received most of them as Christmas gifts, ironically). I've watched all of his TV specials and (I think) most of his live performances on YouTube. Right after he died, I spent the better part of a week watching every piece I could get my hands on, show after show, one bit after another, for hours on end. At that time, there was so much discussion of his legacy and his message, with people comparing his later material to Lenny Bruce and Bill Hicks. I can see the resemblance to both of those guys, but I have to agree with KuriousOrange, Eddie Dane and others that he may have ranted and raved like a maniac, but he never actually ran off the rails into the crevasse of blatant CTism.
George Carlin strenuously insisted that the American people have gone soft on consumerism and been led astray by a cadre of ambitious rich and powerful interests, but he never lent credence for a minute to the vapid ravings of 911 Truthers or blatantly called the Kennedy assassination a government conspiracy. He wisely cautioned us not to believe outright anything spoon-fed to us by our government, but always to question and doubt, and to realize there's always some significant something that we're not being told. He's like my grandpa warning me, "don't take any wooden nickels."
I'd say his political views were definitely extremist in the sense that they acknowledged and focused mostly on just how fractured and rigged the entire system is. His message was certainly alarmist. His was a harsh skepticism, one that shared a long border with cynicism. One gets the impression his worldview was grounded in some difficult lessons learned the hard way, but tempered by an appreciation for the true beauty and awe of life and a genuine compassion for the plight of the average people. For all of George Carlin's acerbic vitriol, a sincere compassion seemed to resonate through the bombast. In that way, he was a populist in the most classic sense. Hearing him speak, you get the feeling he's really on your side, on our collective side. He clearly comes across as a champion of the little guy, bellowing the battle cry to take the fight straight to the arrogant, soulless money-grubbers and all the corrupt powers-that-be they've bought and paid for. Was he an advocate of class warfare? Certainly, but was he a Marxist or a socialist? I don't remember ever hearing him openly advocate for communism or collective ownership of the means of production.
As much as I admired the guy, I'd hate to think he'd given himself over to the weak conspiracy logic. If he ever did, I'd have to acknowledge it with a heavy heart. So far I haven't seen any evidence that he did, but not for any lack of exposure to his material.