Interesting thread. I understand completely the concern about privacy rights, and the hesitancy about "turning someone in" who wasn't hurting anyone, and has no record of doing so. It almost seems like you're convicting someone, not for committing a crime, but for "thinking" about that crime. Look out for the Thought Police!
But in this particular instance, I would look at the potential for doing massive damage to other people and property - by ACCIDENT. You can't really compare it to firearms - if someone has an "accident", they usually end up hurting themselves, or one or two others. They have to be doing something INTENTIONAL in order to cause a mass casualty.
Explosives, on the other hand, are different (you can also fill in here "plutonium", or "Ebola Virus", or the like). Take it from someone who spent 10 years as a Combat Engineer in the Army, and had the opportunity to deal with explosives measured in tons, not pounds - the slightest mistake can kill many. And being careful while fully alert and sober is tough enough, never mind when you're drunk!
I don't like ratting out victimless crimes - if you want to cause your own self-destruction, that's up to you. But if you are doing something that has the potential to cause MASSIVE damage if you're not careful, I think I should have a say in things.
That's my opinion, and I'm sticking to it.
Carry on.