Jumping red lights for no reason is out of order - however, there is a very genuine reason why us cyclists (those of us who are conscientious enough to stop at red lights) begin cycling before the red light turns amber.
Motorists do not see cyclists. It really is as simple as that. I have lost count the number of times I have legitimately been waiting at lights, proceeded as they've gone green, and then nearly been splatted by some complete dick head turning left who hasn't seen me. This is why I go before the light turns amber or green.
It is similar when I am on my motorbike - car drivers turning left or right out of a side road DO NOT SEE MOTORCYCLYSTS: in the past month I have had two occassions where my rear wheel has left the tarmac because of dick head car drivers and I've had to slam on the anchors.