Sure if a hunting rifle was used to kill someone then the manufacturer wouldn’t be liable. Killing people isn’t the primary purpose of that kind of firearm.
But a gun that’s primary purpose is to kill people and is marketed as such? Yeah they should be liable for that.
If they are marketing guns for home defense and not making purchaser of the firearm aware that they’re statistically more likely to kill themselves or a family member than ever need the gun for a burglar, that seems like negligent behavior to me.
Also if they’re marketing anything other than a shotgun for home defense they are creating a dangerous situation unnecessarily. Suggesting someone should fire a weapon which has bullets that can penetrate through the drywall inside a house while the person firing is scared leads to all kinds of foreseeable life threatening scenarios. Shotguns exist, they would be better suited for this (extremely rare) scenario. If they are marketing anything other than a shotgun for home defense they are needlessly putting people’s lives in danger.
If people approach this logically (without the standard gun nut wackiness) then yeah there’s a lot of negligence going on, possibly gross negligence.