Oh for fuck's sake take them up on it. I hate people who make empty threats and don't follow up on it. 99.9% of the people making these fucking lists probably won't even use their gun against the burglar in their house, and most of these idiots won't join the army to protect against any actual instances of treason or attack against American soil. I say, call these fuckers out, give them a place to march with their guns and their empty threats, clear everyone else out of the square, and televise the whole fucking spectacle to let the whole country see what unhinged, idiotic lunatics they really have become.
And yes there's always the tiny percentage that will shoot shit up, the Wade Michael Pages of the world. But sadly we can't identify all spree killers BEFORE they go on a rampage (we can for some, but not all), we can only deflate the sentiment and hope the crazies go die with them.