Ever seen a default ubuntu splash screen/wallpaper on a train, coffee machine, airport terminal kiosk, bus, or other big piece of slow moving, appliance-y thing?

That is why Ubuntu Core (and similar) exist. More secure, better update strategy, lower net cost. I don't agree with the licensing or pricing model, but there are perfectly good technical reasons to use it.

Not if the end user is an operator of safety critical equipment, such as rail or pro audio or any of a number of industries where stability and reproducibility is essential to the product.

That's because it is a net negative to the end user and to society at large.

If the end users do not want the net negative, maybe they should pay for the security features instead of expecting everything for free.

I don't understand. The user will not have a choice.