before you exercise you have to warm up your muscles by stretching and so forth, in order to avoid causing muscle strain, pulled muscles, stitches, muscle cramps etc... why then should it be any different to warm up your vocal cords before singing? Warming up prevents vocal injury, straining your voice or ending up with nodules and unable to sing again. Do what is best for you not what people think. At the end of the day it's your body, your choice, your health not theirs