Nobody has, or would, argue that taking off directly into the wind is not the preferred scenario. But you're overcomplicating things for yourself (and others) - straight downwind takeoffs are perfectly fine if you achieve sufficient airspeed, AND if you account for wind shear as noted by having a safety margin. In most model aircraft takeoff scenarios, there is about 18 times as much runway available as needed at a bare minimum. And in general our power to weight ratios are large in comparison to typical full scale, AND we often have gobs of control authority. So we can "get away" with a lot it seems at times. In the end it all comes down to understanding the situation, and having the ability through experience to judge the model's airspeed by interpreting the information reaching your eyes in combination with some idea of what the wind speed is.

A good RC pilot can, assuming the runway is long enough, make downwind takeoffs all day without worry. You need to remember airspeed is all that matters to the aircraft. Since the aircraft has mass, and a finite amount of thrust available, when the goal is to accelerate from zero to 25 mph "ground" speed it is going to (as already pointed out so sorry for repeating) take a longer time and consume more runway to achieve the required airspeed. But it will do so given the chance. And once it is at airspeed, it's flying exactly the same as if making an upwind takeoff.

Yes... the odds of screwing up and cartwheeling your aircraft are higher in a down- or crosswind situation - that's completely obvious. (Mind you some people manage to do that when taking off into the wind). The magnitude of the cross or tail wind has everything to do with the amount of additional hazard. It is also correct to say that under reasonable conditions an experienced pilot can make those takeoffs with the same security as an upwind takeoff - because the pilot is aware of the issue and fleis with safety factors in mind. As the magnitude of the wind or gustiness increases, then the potential for problems increases accordingly. Cross winds are always a hassle, and strong crosswinds can cause anybody to have a bad day. It is a really good idea to practice cross wind takeoffs with that ol' trainer you have kicking around until the inputs and reactions become second nature. That goes for any flying skill of course, but some things often get less attention than others during a pilot's development (like rudder usage). If you trim said trainer for a very gradual liftoff and climb on it's own under full power, then you have a good practice tool for downwind takeoffs too - keep it straight with wings level and just let it fly off on it's own and carefully observe the apparent difference in speed caused by the addition of the downwind element, all the time remembering that the aircraft is, as far as it is concerened, flying in the same manner as upwind and seeing the same relative wind. Do that a few dozen times and you've probably learned something. You can do the same for crosswind situations too - trim it out as mentioned, then concentrate on maintaining heading and wings level. I wouldn't suggest starting on a day with 30mph gusts however..

MJD