Erm, the airlines specifically tell you to pack fragile / valuable items etc. in your hand luggage, so presumably they agree with the premise of others understanding that something in your bag could be fragile / delicate. Heck. Maybe you are happy for someone to put their leaking meatball sub on top of your belongings, or slam their overweight oversize rollaboard on top of your laptop (seen both happen to other people, resulting in a smashed laptop screen and flying tempers, and a suit carrier and its contents covered in red sauce), I however am not. And if I got to a bin where someones things were already in there, even if there was space, there isn't a cat in hell's chance I would put my bag on top of someone else's items. It is just rude. Shared space is one thing, a blatent disregard for others personal property is not. In the vast majority of cases, all it takes to get everyone's things in the overhead is some spatial awareness, and a ex-tetris addiction - all without piling things on top of each other.

I suppose I could buy a much larger carry on bag, but then it would increase, not decrease the problem, as most of the time I try to obtain a bulkhead seat, so instead of my handbag and jacket going on top of my small case, I would need to take up even more overhead space.