It's hard to argue with this really, but some people do. I personally think that there is nobody better to comment on a topic than someone who has studied the topic and become a world expert. Use caveats etc, and for goodness' sake make sure you look at - and weigh - the issues outside the science. But once you have a well informed opinion, share it. You're a scientist - be open to other ideas, and be willing to modify your stance if new information is presented, but still - say something!
After all, if you don't, then people who do not know (or care about) the facts will say something. And they will carry the day.