You are quoting him out of context. That was directed at wannabe-writers who don't make time to read. Which is completely fucking batshit crazy. If anyone deserves some f-bombs, it's them.
Additionally, the very next sentence is "Joking. I would never say that. But I certainly fucking think it."
Who exactly is the advice for? For those who don't read, right? In that case, how does abusing them help? There's another golden rule about treating people the way--can't quite recall it, hmmm...
Casual obscenity has become so normalized in the culture, you probably feel outraged I'm even bringing it up. Not reading has also become normalized in just the same manner. No one reads if they can at all help it-- not at work, not in parks, not on the commute, and not for writing. Their loss, of course.