"If you had a twist throttle and you hit a bump, you tend to twist the throttle wide open. Dangerous."
Not really, it depends on how stiff the throttle is, and on most occassions it won't happen unless you're cranking it.
About all those accidents with the hill climbing and stuff, maybe they need to learn how to ride before doing things like that!
I myself prefer the twist throttle, because when you hit a tabletop or large jump, your thumb would probably give more throttle on a thumb throttle, and I don't like my thumb being sore after 30min. of riding!