How far behind a car going uphill in snow would I be? Given your lack of detail of the situation, it's impossible to say. I'd be far enough so that it wouldn't roll back into me, but that is neither objective nor rational.
I agree that nothing can be done *after the car has lost traction*. But the act of losing traction in the first place, and therefore not being in control of your vehicle, is your fault. End of story.
To simplify, there are three relevant variables. Your car, the road and the car behind. Nothing changes with the road or the car behind in the time it takes to have the accident (yes, the road conditions are bad, but they were bad before you lost control). The only change is your car going from being under your control to not being under your control. Therefore it's your fault. Perhaps the car behind could have been further back, but this does not make it their fault. If you slide backwards into them, it must be yours.
At what point is this argument not objective or rational?