1. A minor dusting like this week is a 1 in 100 (or 50) year event. This falls out of living memory, and there hasn't been anything like this since modern aviation took off. There should be some preparation for these events, and this can save billions.
2. Some consideration should be given to the 1 in 500 year events. These are devastating earthquakes, like Lisbon. In most cases, all you can do is quickly clean up. For Iceland volcanoes, we're talking a 'Black Death' event.
If no consideration is given for the minor events, then the worst thing is over-reaction. They set their tolerance for volcanic ash to zero point zero, which is a lazy thing to do. Just shut down everything if there is a volcano! But the weasly toadies started to change when the big boys were inconvenienced. Then they knocked the target up to some random level that allowed executive jets to fly.
Had they done something in advance, it would have been an easy matter to set some physics-based levels. What level clogs up a jet engine? What level just shortens life between tear-downs.
Are the toady regulators this bad in other areas? You bet! Right here in Ontario, they are ready to shut down all the nuclear reactors with a significant 1 in 100 earthquake, since this will ravage the power grid system. The toady regulator hasn't got a speck of credibility, yet when we are all freezing in the dark, and everybody is dying, they will allow the nuclear plants to start up without inspection, and without any criteria. Or will they? Has any regulator allowed a nuclear plant to start up willy-nilly after an earthquake? Most likely it's 6 months of inspections. This will be just as interesting as Europe!
Of course, we haven't even approached the 1 in 500 year events! There won't be an over-reaction, since it will be horrible. Again, some planning, such as building codes, will work here. For Europe, they better develop a good ash filter for trains and trucks! Forget the planes!