Of all the things they have banned on planes, this makes the most sense. In terms of simplicty, a lighter and a can of hairspray has a whole lot of power to do damage. Now, of course, if you light off a can of hairspray, you're going to have a cabin full of noxious smoke - and the cabin doors are locked, so you're not going anywhere.

However, imagine if the goal was not to do anything more than set the interior of the plan on fire and kill via smoke inhalation. That's not an unrealistic scenario and would be a kind of terror attack that fits the MO of Islamist nutcases.