And keep it light and easy. I've never been to a SciFi con, much to my dismay. If I could go, I'd want to be entertained.
Start with an HB statement:
"The Van Allen Belt would have fried them". Chuckle a bit, and then give the explanation. Get the audience in on the joke.
Destroy the arguments one-by-one in this way. First give the HBer's argument (use a nice low serious tone), and then rip it apart.
They're in their 20's and 30's and science literate? They'll get a kick out of it.
Lisa