Ive been in the freighter's on and off for over 20 years and have driven through lots of stuff. Mountain wave's, clear air turb and so on. Only a few times was it severe enough ( in the freighter ) that we took action and asked for an altitude change.
Once on the L-1011 it scared the crap out of us because we lost several thousand feet over the mountains and it was a wild ride. While flying Pax we always asked for an altitude change at the first sign of bumps cause we had to. My point is..that most of the time it really isn't that bad to the experienced crew however, a passenger can get quite rattled over it and even more so when 50 or 100 pax are all rattled and screaming at the same time, then the turbulance is at it's worse. Also it dosen't take much to launch an unrestrained and unsuspecting human into space ( or the overhead bins ) so that's why we all should
wear our seatbelt's all of the time !!! 
Please don't flame me if you think I,m making lite of this particular incident cause I,m not.
Just making a point.
