Seriously though, this is like holding some one liable if his car is stolen and used as a get-away car in a crime. It's also not really possible to get a shell on most of these devices with serious effort, so apart from turning one off, I'm not sure how any one is supposed to mitigate this. They're too locked down to do any kind of disinfection, in most cases. I guess now I have to teach granny to use a uart cable, too.
It's not easy, but it's not impossible. I could envision a software based solution that approaches simplicity in installation.
What I'm not arguing, is that someone should be held liable for their devices being used in a botnet.
I believe the manufacturers and retailers have the liability. But I am definitely not a lawyer.
You don't interact with people out of your bubble much, do you? It's time to start write better code, not blaming users for the programmer's incapability.