Some of us see it as, drugs being something that one inflicts to oneself, while weaponry, assassination, terrorism and manufacture of pedophile pornography is, in contrast, inflicted to others by force.
Weapons are like drugs, they don't necessarily hurt anyone unless you plan to invade my home or threaten me. Assassination implies that the sole goal is killing a target, buying a gun can be for protection, for a collection, for fun and hobby, for sustenance, ect.