I don't think your drug analogy is right, there most certainly are laws that mandate secure storage of dangerous items, explosives, animals, chemicals, etc. A more apt one would be an explosives store owner that locked their front door but didn't store their explosives in a safe. If someone broke in and stole the explosives wouldn't you expect the owner to be in big trouble?

A significant number of guns used in crimes are stolen, so its too bad that more gun owners don't believe in secure storage like you do. I don't get your "slippery slope" comment, could you expand on this more?