There is nothing unhealthy about peanut butter (when I say that I mean ground peanuts, not the brands with an insane number of additives), but almost anything in extreme quantities can be toxic. Even water.
The human body is meant for variety. It's wild that as much as we've learned about the absolutely insane importance of the gut microbiome it still comes down to "eat your vegetables".
drinking six liters in three hours has caused the death of a human.
That sounds like a very small amount in three hours.
I had a situation when I was stuck working in a very hot engine room. I went through a gallon in an hour and got Ill afterwards. I still don't know if it was the heat, water or a combination.
Either way, I did learn that if I get in a situation where I'm so hot that the sweat is running, the answer is to cool off, not just slam water.