Look in the references: "Four additional studies found post-LSD psychotics with prior psychosis but also patients in whom the drug precipitated psychosis without a prodrome ... One group reported cases of psychosis following a single dose, suggesting a peculiar vulnerability to the drug in certain individuals. A review of this problem concluded that prior illness was evident in many, but not all, psychoses following LSD "

Your general gist seems to be correct (that it's a rather low risk for people without history), but "no one" seems to be incorrect. Which makes sense - LSD's a powerful medication. And for comparison, this happens with stuff they give to kids, like Ritalin and speed.