The way I interpret the idea is that exposure to BASIC is kind of like lead poisoning.
(1) Age of introduction (younger you are, the more damage it will do)
(2) Sustained exposure (the longer the exposure, the more damage it will do)
(3) Amount of exposure (writing 10 or 20 liners is not as bad as writing 2000 liners in BASIC)
Just like lead poisoning, there is no safe exposure tolerance to BASIC. All the minute amount of lead in the air from decades of leaded gasoline use is killing your brain cells, even little molecules of it - as we speak.
Too much of (1),(2),(3) and you'll probably end up like SpectateSwamp or something. Damn, that might explain it. Or it could be real lead poisoning.