The gun company will claim they sold for self defense or just for a hobbyist's collection - They'll claim that the gun owner used it for something else is not their responsibility. Same for any or product that can be used to kill someone with.

They absolutely can be held accountable. The Protection of Lawful Commerce in Arms Act (PLCAA) has carve-outs for: negligent entrustment - when a dealer or manufacturer provides a firearm knowing it will be used for a crime; negligence per se - when a seller knowingly violated state or federal laws in the sale or marketing of the product (and that sale was a proximate cause of the harm); defects in design; breach of contract/warranty.

However, selling a product for lawful use, whether a gun, truck, or Internet connectivity, does not make the seller liable if the consumer decides to use that otherwise lawful product for crimes. There has to be some assumption of agency (and liability) on the part of the individual who is clearing ethical/moral hurdles to do wrong.

I don't see how this unanimous court decision conflicts with that theory in the context of the ISP - in fact, I think it's a reinforcement of some common sense.