We are talking about tree climbing not rock climbing. The weekend yuppie thing doesn't ring true to me in the tree climbing world. I'm sure they're out there but all the tree climbers I know are good people who climb trees for a living or climb trees for the love of it, or both. It's all good.
Anyone who wants to use ascenders to climb trees had better get good training from an experienced climber. The gear we use isn't designed to protect the person who walks into a store, buys it, and goes out to climb without training or thorough self edumacation. I can think of an easy scenario for a person to kill themselves with just about any piece of gear. Equipment designers can only go so far in protecting the untrained user without making the gear unusable for experienced climbers.
In the "accident" involving the Petzl ascender, the instructor was clearly at fault. They are ultimately responsible for the safety of their student. The instructor put her student in danger when she let him go up with the cam release facing against the rock. That's probably why Petzl won't acknowledge her claim of defective gear: operator error, case closed.
-moss