I think Sunfish's argument is based on the fact that airlines sometimes do things which are not necessarily optimal for safety,
What like flying in areas of thunderstorm activity, like flying approaches and departures with surface winds above 0, like flying in the bird migration seasons or into and out of coastal based airports etc etc etc
Safety has to be based on a demonstrable threat there is no demonstrable threat from a light ash encounter only a percieved possible threat. There may be ??? a financial cost threat but as yet not even that is bearing up to scrutiny.
Pace