Huh? Ban guns? Where did that come from? That's a flawed analogy.
Oh, so you just talk with them and ask if they were serious or not. Someone makes death threats on the internet. They're asked if they were serious? Oh no! that person replies. A few days later there's a killing. Yep, that'll work.
And the neighbours say, that person was such a nice person. Always so nice and didn't make any trouble.
Everything is a flawed analogy. Want another one?
You wife makes you lunch. However, if you anger her, there is a chance - however small - that she might poison you. After all, that happens, you can see it in the papers.
So let's ban all angry women from making lunch on the off chance that one of them might poison you.
Over-bloody-reaction.
I ask you again - how many internet threats ever amounted to anything? You got a greater chance of being struck by lightning.
Do you flinch and run away every time a lighting strikes?
and b.t.w. - the people you should be worried about aren't the stupid ones that will post stuff like that. This guarantees they will be caught if they try anything. A smart person that wants to kill you will stay silent.