Suppose you were working on an early mission-critical computer system. Your coworker is thinking about a potential security issue. You say: "Yeah I read about that in a science fiction story. It's not something we need to worry about." Would that be a valid argument for you to make?
It seems to me that you should engage with the substance of your coworker's argument. Reading about something in science fiction doesn't prevent it from happening.
In this analogy it's not your coworker. It's some layman (despite self-declared expertise) standing outside and claiming he's spotted a major security issue based on guesses about how such systems will work
From what I have observed the reaction of most people working in the AI to "What do you think of Yudkowsky?" is "Who?". He's not being ignored out of pride or spite, he just has no qualifications or real involvement in the field
It seems to me that you should engage with the substance of your coworker's argument. Reading about something in science fiction doesn't prevent it from happening.