Sure a modern aircraft can fly with a load of contamination on the upper wing surface.
Problem with this sort of attitude is that it displays a stunning lack of awareness of what is happening aerodynamically to the wing. Adding snow/contaminant to the wing does several things, of which two are vitally important: a) it adds an undetermined weight to the aircraft, b) it changes the aerodynamic properties of the wing.
So at a critical moment of flight, takeoff, your performance figures are rubbish. You normally rotate at approx 1.2 Vs for the weight and given performance of the wing. So, an unknown amount of weight has been added bringing you closer to Vs, at the same time the wing performance has been degraded at an unknown rate. As you rotate you are asking more of the wing as you increase the AoA, pushing you closer to the stall.
As a wing stalls the centre of pressure/centre of lift moves rapidly forward on the upper surface of the wing causing a pitching up movement, again increasing the AoA. So at the stall you pitch up - you don't know the stall speed due to extra weight and degraded wing performance. And it gets worse - the previously clean and identical (or as close as makes no difference) wings, are now contaminated to differing degrees. So the wings will stall earlier and at differing times. So just at rotate, you raise the nose and stall ONE wing causing a rolling manoeuvre with low airspeed and high AOA - the perfect conditions for spin entry. You won't spin of course but the half flick roll into the concrete is usually terminal.
This is exactly what happened to the biz jet at Brum a few years ago.
If there is contamination on the wing DO NOT GO.