As with most things security: expecting security to be the problem of the other part(y|ies) is a recipe to security problems. Airlines need to make secure systems and processes, passengers need to try to protect their information. No amount of "well I'm the paying customer" means you completely stop playing any role in your own security.

I.e. saying you should be careful with how you display your boarding pass isn't the same thing as saying the airline's process has no blame.