Despite having had the relevant experience, I've always found it hard to understand why this happens. You know you're taking a drug that reliably induces feelings of "oceanic connectedness". Why should you change your worldview as a result? All kinds of things can change the way you feel temporarily, but most of them don't leave you thinking that you got insight into the way things really are. Maybe it's that psyched…
I believe it's because it shows you that reality is not actually real. It's just a product of your senses. During a psychedelic trip, one might wonder "if I had been like this all my life, I would consider this to be reality, not what I'm used too". It fundamentally shows you that what you consider reality might be very, very, very wrong. So how can I trust my own senses and perceptions if they can be so powerfully m…
The only explanation that doesn't lead to absurdity is that drugs corrupt your perception. They interfere with and frustrate the healthy and proper operation of the brain and in doing so distort perception.