Oddly enough though, I feel that if a geneticist (or company) were to irresponsibly create and release a genetic line of highly invasive, quick-breeding, destructive rodents that wrought havoc on a large percentage of a city/area/state/country/etc., and people knew the source and knew who was responsible for the creation of these animals, then I think some sort of recompense would indeed be sought, or at the very least, blame cast, and an attempt made at justice of some kind being exacted for damage caused. Is this not a better analogy (especially given your idea that god is "very much above and beyond such things") than the parent to child idea that you brought to bear? Not to mention that parents can be very responsible for children under a certain age, and when those children become adults, then they are basically the peers of their parents, and are more equal "agents" acting upon the world of their own volition - hence the reason they become responsible for their own actions.
Guns are a different matter, because they have actual application beyond the violence they are sometimes used for. Just like a knife or a car can be used to commit grievous acts - and yet we hold no person who created these things accountable - because it was not their intent that their product be used this way. However, if a company decided to craft a gun that had a sight built onto it, within the reticle which was the silhouette of a human head, well, then things might be different (responsibility or blame-wise) if we started seeing people using these weapons against other civilians, don't you think?