I guess you cannot take that threat seriously. It is just a flight of fancy... Everybody is hoping somebody else is stupid enough to actually do it!
Nobody wants to be the nutter who actually does something that epically heroic! We all have too many responsibilities. Whoever does it would need to be without dependants in case he/she takes a fall. They will need to be clever not to turn the highway into a crash site with people plowing into downed gantries at high speed. The liability is massive! Romantic idea but it will never happen!
Nothing wrong with wishing harm to an inanimate object like a toll gantry! **** those who think otherwise! It is only problematic when you consider hurting people...