I don't disagree in principle, Pace, but I will accept short time windows where there is very low cloud (or fog) in the context of a long flight.
My reasoning for this is that it is not practical to avoid it comprehensively.
Let's say you are doing an 800nm flight. The only idea you have of surface conditions (in any reliable sense) are METARs obtained immediately before the flight. A few might feature fog or low vis etc but they are only reporting conditions within a very limited radius of the aerodrome, and your glide distance from say FL150 is going to be way longer than that.
You could get the
UKMO visible image which will show fog banks, but only if the conditions are otherwise blue-sky. And there is no way to use this to distinguish between solid fog and a layer 3000ft thick with a 1000ft base, because the tops temperatures will be very similar. Nevertheless I have used this image to see what a large chunk of coastal fog was doing, on an otherwise clear day.