Borys, I support you. Here's why.
On several trips between Northern and Southern France, I've reached 1,000m above sea level and seen snow/ice on the roads, having to drive gingerly whilst shod with summer tyres. Yet before setting off, I never saw any forecasts of sub-zero temperatures or ice on those routes. I know this because I always check in order to not make the trip, or to do so on the warmest and driest day of the five-six day forecast. In every case where I travelled and yet saw snow/ice, the forecast was for temps above 3 Celsius at the lowest. I know enough about altitudes and temps to know the figures will be a few degrees lower than that. If I'd had winter tyres for some of my trips, I'd have saved probably an hour each way!
During winter three years ago, late at night, I had a scary moment in Northern France, about 30-45 mins before the tunnel (so not at altitude). Travelling at 80mph, I was passed by a French registered car and we were shortly hit by hailstones and icy conditions. I lifted off and braked gently to probably 40mph. My outside temperature gauge quickly moved from +3 degrees to -1.5, and the car that had passed me came off the road ahead of me. Luckily, he didn't hit anything. But thereafter, we continued at about 20-30mph for about another 10km, before emerging from the hail into sleety rain, and a rise in the temp gauge back to about 3 Celsius. I really wished I'd had winter tyres on that night. No forecasts for my route suggested this kind of event, nor sub-zero temperatures. Maybe it was a freak, but I doubt it - because I recall there were road signs warning of the danger of skidding cars and of ice.
You sceptics can search as high and as low as you wish for evidence to refute Borys' posts. I believe him. You're unlikely to find a forecast to match the conditions on the road as some of us have experienced. I know that I never ever set off on any of my long French trips when temperatures are forecast below 3 Celsius, day or night. Because I know the reality can be lower, and will certainly be so when I get to altitude.
Now, with Conti winter tyres on the W203 I drove so often through France, my big headache isn't making progress in the winter in the UK. It is knowing that most drivers around (mainly behind) me think I'm on summer tyres, and will assume they can match my winter tyre grip levels on their (likely) summer tyres. I had several near misses last year where cars clearly lost traction and skidded towards me or the kerb as they tried to keep up with me, especially when they took bends alongside me. So now I drive far more gingerly with my winter tyres on than I know I can (tested the limits last year). I also brake earlier to give the optimists behind plenty of time to avoid hitting me.
You don't have to have them on. And you don't have to believe in their merits. But it'd be a reasonable thing to expect that some of you'd just stop trying to discredit every post on the merits of winter tyres, just because you don't believe in them.