I wouldn’t fly through that crap, pitot tubes can become clogged, that grit is like sand paper in the engingines and all kind of other crap can go wrong.
Flying isn’t 100% safe in the clearest air, which is the guy’s point.
Obviously flying through that is normal but the problem with this ash is once it disperses it looks just like haze or light clouds yet it still has all of the destructive properties. I'd hate to be the one who has to make the call when it's "safe"
The post that I responded to seemed to suggest that there was some other objective or motive other than safety to keep planes from flying.
Just my take on it.