Banning things is always a difficult and dangerous proposition, no matter how much harm those things can cause if misused. For guns, knives, drugs, and other m

Banning things is always a difficult and dangerous proposition, no matter how much harm those things can cause if misused. For guns, knives, drugs, and other more routine contraband, law enforcement action required to maintain such bans have their own costs. Law enforcement can at best selectively enforce such laws, because contraband is almost always hidden. As a result, privacy erodes as politicians and law enforcement want more ability to discover who has contraband. If something is harmful enough and also rare enough or requires substantial skill to procure, like nuclear weapons or biological weapons, then there's the argument that banning those things improves the safety of society. I am not convinced that the legality really matters; the economics of procurement provide a strong barrier to random ideologues and nutcases from procuring such weapons, and if they can anyway it's doubtful laws would stop them; there's also much more opportunity for anyone along the logistics chain to notice something strange about their buyer and report it to someone, even if the transaction were legal. That can't be done with firearms or knives with thousands being sold a day. However, the consequences of nuclear and biological weapon use is so horrific that despite the economics, it still might be in everyone's best interest to leave them effectively banned.