Not in any way condoning the actions, but "child" in that tweet is a bit of a stretch. The victim was 17, so could legitimately have been married, a father and driving license holder.
I cycle in Mid Sussex and That London daily (including today) and would estimate 80-90% of cyclists adhere to traffic lights.
Of those who don't, it's mainly people pushing their luck on traffic light changes, rather than sailing straight through - albeit yes there are some of those, more than...