And unfortunately, as long as there is ash in the air, the usual highest level of safety is not being maintained, although the revenue stream of airlines is being maintained.
Well, you can also say that the highest level of safety is not being maintained as long as there are planes in the air.
Apart from safety and the revenue stream, the needs of passengers are important too. Thousands of pax are having their business and vacations ruined, and lifetime wasted.
Let's see, a life expectancy of 80 years means 30000 days. If a pax gets delayed by 3 days, he has lost 1/10000th of his lifetime. Sure, some will enjoy the unplanned extra vacation, but I am pretty sure that for the majority of passengers, this is wasted time coupled with extra expenses which will make their life worse in the future. So for every 10000 delayed passengers, one life is practically lost by such a delay (and we are not even talking about actual health damage due to stress, lack of medication etc.).
If flying through ash means bringing pax to their destinations 3 days earlier, it pays off even if one plane in 10000 crashes because of a higher danger level.