Consider fighter aircraft on a strafing run to be Lewis Hamilton at top speed in his Mercedes F1 car and a civilian airline on final approach to be a double-decker bus going around Marble Arch. A weapon system that can shoot down a fighter aircraft is going to find shooting down a passenger jet as difficult as hitting Jo Brand at 5 feet with a shotgun.
If you're talking advanced anti-air then yes, I would expect a child to be able to push the right buttons and take down a civilian jet. What I thought we were discussing were not TOW, Laser-guided or Stingers but your standard high-calibre machine guns and cannons that frequent militia cells scattered around the Middle-East and Africa
from Russia (with Love etc).
Civilian aircraft are travelling at around 150MPH at landing (vastly losing speed though), so some target leading, and perhaps elevation - depending on positioning - would be required. Take-off is highly predictable too, with the added effect of potentially accelerating into the projectiles - they would be utterly catastrophic against a civilian aircraft and it would tear itself apart or lose lift long before it reached an altitude where pressure, temperature and oxygen would be a consideration.
Civilian aircraft is rarely targetted though - they have no idea who is onboard and the impact on their region can be horrendous in terms of escalation events.