VT Shootings- Some thoughts

I am not saying that is no European home where the occupant has acquired some extra ammo for their service weapon.

What I am saying is that your implication that a large number of households have military weapons with available ammo is incorrect.  I know of NOBODY that has ammunition they could use in their weapon - in fact, most of them intentionally keep their weapon disassembled and separated far from the ammo, to avoid accidents.  It's not just a matter of ammo availability, but of mindset.

Are there one or two exceptions out there - probably.  But your portrayal of these nations as vigilante-ready is factually incorrect.

There is an obvious way to check - look for instances where any European, from a country where weapon+sealed ammo is issued, has used their service weapon (loaded) for any purpose at all other than authorized drills.

I haven't looked.  I encourage you to.  You may find one or two incidents with nutballs, but if your theory were correct there would be a large number of incidents, and without nutballs.