I'm sorry to hear that your son's bike stolen. It's frustrating to have to ugly-up a bicycle to deter a thief. Maybe it's a girl thing, but I love making my bike pretty... I've been a driver as long as I have been a bicyclist, and I've never cared about the type of car I drive, am lackadaisical about keeping it running, don't wash it, and it was broken into and I was like, meh, nothing was taken, because there was nothing to take (with 4 kids, though, I know I should keep it).
But with my bike, I am a total mother hen over her... she runs smoothly, looks good, and I want to keep her that way... she's inspiring to ride and take places and make memories with my family.
So, I guess, for now, I'm focusing on locks as my way to keep her safe... maybe I'll get a milk crate for the back, because it's practical and will "ugly it up a bit," but even that one is a tough one (it would cover the beautiful wood seat top on the rack)
P.S. I'm not upset with you/your suggestion, just frustrated that a thief makes us spend more money on locks and/or we have to uglify our bikes just because there are morally-defunct thieves, et al.