Sorry but this is just a myth that is continually perpetuated by people who don't know how materials work. Aluminum is a soft, relatively pliable material. It's failure mode is often a tearing action rather than a breaking action. I've broken aluminum frames and parts in the past and not one of them has shattered like most people think they do. I've run an aluminum crowned mountain bike fork into a curb at 30+ mph and the crown bent backwards but it didn't crack or break or shatter. Most of the time when aluminum does crack, it will creak and groan and tear before it fails. My aluminum frames that broke and lots of rims that have cracked down the middle all made lots of noise before I noticed that they were cracked.

Steel parts and frames that I have broken don't crack nor bend nor make noise nor tear. They broke. No warning, no cracking, no bending. Two mountain bikes broke at the dropouts by snapping suddenly...one might say catastrophically. Pedal axles have sheared off without warning. Spokes go 'PING' and they are broken. Wheel axles have also broken suddenly on me. And it makes sense. Steel is a brittle material and stiffer than aluminum.