I still think it's appropriate to send children off to play by themselves I'm afraid, but then I often find myself apart from current thinking in some cirsumstances.
However, something like 30 years ago I was doing my PPL. With an instructor, God bless him, who told me in no uncertain terms more than once that it wasn't OK to go for it if there was so much as a squashed gnat on the wing, let alone some snow.
He was qute right then and he still is now.
Whichever way you look at it, the reason for the crash was contamination on the flying surfaces, and it's been the reason for a number of fatal incidents. It wasn't permitted or excusable then, and it isn't now.
Enough lives have been lost to make this a point that never needs to be debated surely.