One problem I see with your analogy is that the dangerous lawnmower can cause an easily quantifiable harm.
You have to be able to show damages you incurred and assign a dollar value to them to sue people.
That doesn’t work at all for a something that sells your bandwidth to a proxy service. People wouldn’t even be aware that it was happening they weren’t told.
What about when the police show up because some highly illegal content was traced to your IP address? Will they believe that you were the unwitting victim of a rogue proxy server running on your streaming stick? Would you have even been aware of that possibility?
There's also always the flip side: When the police shows up because of your illegal acitivities, you have a rogue proxy server running. All bought in good faith of course.
Not legal advice.
(It would surprise me greatly if we as a society let these gadgets be sold openly from here on.)