Mixture
So are helicopter rotors, mountains, skyscrapers, electricity pylons, TV masts, wet runways, cigarettes, alcohol.... where do you draw the line ?
Do you think everything in high-vis jackets, flashing lights and warning notices is going to solve the world's problems ?
Are you actually a pilot? If your argument holds true why bother with high intensity lighting on top of buildings like Canary Wharf far easier to see than a pencil thin crane towering into the clouds above it?
Yes but.... what good is a strobe/light in the fog/cloud ?
As I said earlier, the diffused light will do nothing to help an already disorientated pilot.
A strobe is visible in cloud remember visibility in in cloud varies from around 50 meters to 200 meters and sight of a strobe in such a situation would mean the pilot pulling instantly away.