The canonical risk of canning is botulism, which is fairly rare but bad enough that anyone who cans should be aware of how to prevent it, and everyone should know about not eating from things with swollen lids etc. Also we now have an antitoxin - that's relatively recent. (Still not great for you if you get it though.)

I think the thing with doors unlocked is it really only takes one burglary for one to decide that locked doors are a great idea. And rural areas mean there's less people around to do the burgling but also maybe less people around to see someone acting shady. We do have definite evidence that the more crime you hear about, the more crime you think there is, and this is why a lot of people think things are awful right now even though crime has been trending down for decades.