Should is irrelevant. People shouldn't spill on themselves. It didn't absolve McDonald's from a lawsuit over the temperature of their coffee. Engineers all try to design for the dumbest possible use case. With guns, they aren't trying to meet that standard, and lawmakers have done their best to shield them from all liability. It's nonsense.
From today's NYTimes: http://www.nytimes.com/2015/10/13/us/milwaukee-gun-store-trial.html
Badger Guns was ordered (pending appeal) to pay nearly $6 million to two police officers shot by guns illegally sold to a straw buyer. The owner's son took over the store, implementing a variety of changes: But there are also signs laying out strict rules for would-be buyers: “Must be 21 to enter. Proper ID required.” “No cell phones allowed.” And for the droopy-drawered set of possible customers: “Pull your pants up or don’t come in. Try to have some decency and respect. No one wants to see your underwear.” The rules are serious, Schwarz said: Staff members “will ask you to leave” if you show up with a cellphone. The policy is designed to prevent straw buyers from texting photos of guns to friends outside.Mike Allan’s first move was to adopt a members-only model that requires customers to register with the store and to pay a membership fee. Would-be buyers must also demonstrate proficiency with a firearm....
I think so. Providing a dangerous tool to an unqualified person can be a kind of reckless endangerment to the public. This can be a difficult judgement call (a car is dangerous too), so you might get better results on a legal-case-by-legal-case basis than trying to apply general rules. The coffee-gun analogy is a bit strained, because of the difference in "worked as designed" outcomes. Also, the famous coffee lawsuit is an interesting story, and not a very good example of the need for tort reform in my view. The customer asked for $20,000 to cover expenses, and McDonald's offered $800, then it went to court. Interestingly, McDonald's was already printing warnings on the coffee cups at the time.