IFALPA and the majority of pilots worldwide are against arming pilots for very good reasons.
Maybe the US are different because their pilot ancestors were required to carry guns until about WW2 to protect the federal mail bags.....
If every one of the 100.000 pilots worldwide carries a gun there are 100.000 more guns on flight decks than there are now. Given this number a certain percentage of accidents is inevitable. Sitting strapped to a forward-facing chair you are at a disadvantage against any attacker from the outset, so even non-lethal stun guns won't be a big help.
For some reason the USA don't see the math that the large number of gun-related crimes is directly connected to the easy availability of guns....
BTW, there's a good novel called THE TRIGGER co-authored by Arthur C. Clarke on the subject of firearms.