I think there is an important distinction between somebody (famous) pushing their own beliefs and fighting to improve things.
From what I have read, e.g. more cars RLJ than cyclists ... so why does a cyclist take a public platform to start telling cyclists how bad their cycling is (because they are RLJ'ing). I'd have thought it will achieve nothing for cyclists but will reinforce those poor drivers who think cyclists should keep out of their way and "bring danger on themselves", etc.
From what I've seen of Wiggins, I agree that I don't see him being a good "ambassador" for cycling. He could certainly do a lot to encourage more to take-up cycling, but when it comes to things like safety, regulations, etc. I think he will help those anti-cycling ('cos they get in the way of cars) more than cyclists. And, from what I've seen, he seems to want to expound opinions over those who are already cycling.
Maybe I'm being unfair, but can only form my opinions from what I've seen him do.