Nigel - not picking a fight but you read his post one way and I read it another.
If the vis is less than 1km due to suspended water droplets you are either in fog or cloud and neither is suitable for VFR flight - no matter how good you think you are.
The guy in the accident started out in what he considered to be acceptable vis and wasn't revising his weather decision because he was looking down at the ground or in at the GPS - so when it got too bad and he lost ground contact he was stuffed.