Cadence is not the only thing that needs to be considered if we are talking about preventing knee pain. I don't think it's accurate to say high cadence is bad or causes more pain to the knee. It depends on how much torque you are putting out. If you have little to no resistance and a high cadence, there is minimal stress on the knees. Same with low cadence and no resistance. Now when you start increasing torque, that's what impacts the knees more. Cadence + Torque = Power.