If a missile (ground or air launched) brought down an airliner just think of the lawsuits and possible criminal trials!
It could (and would) be argued that -
it might not have crashed if left alone,
it would not have crashed where it did,
the passengers and crew were unlawfully killed by the missile.
So the government would be liable liable for all the costs, injuries, etc and whoever launched could be prosecuted for murder and/ or manslaughter.
Lawsuits would be launched in many countries by the relatives of those killed or injured as well as by the aircraft owners and insurance companies.
The threat of death would not deter terrorists and they would be delighted if the authorities scored an own goal!
It is all just political posturing.