The crowbar was a metaphor for psilocybin and the like.
I mean, yes, you can have hallucinations that you take for real and are mistaken to believe. But, y'know, there is such a thing as healthy mental functioning, and a real world that we are able to grope towards some fallible understanding of. There's a baseline of rationality that you have to have reached in order to progress to any higher level, but it isn't very high: anyone who hasn't suffered grievous insults to the brain is already there.
Anyway, it's interesting to see this quote at -2, while the George Carlin quote is at +2 although it says the same thing. Surely on LessWrong people aren't merely voting up witty words, and nitpicking anything expressed more plainly?
Your quote seems to state, "Believe everything you see", on a site where people would often agree "Don't believe everything you think". Carlin does not seem to be making the same sort of claim.
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.