Let me throw this at you, PM, aren't these economic issues rather than engineering issues?
On helmet laws, from an engineering viewpoint we can explain what a helmet will and will not do, but from an economics viewpoint it's the cost to the taxpayers (ambulances, cleaning the road of some dude's brains, higher insurance rates, etc.) that might hit home. However, this argument - specifically related to helmet laws - has been publically made (I've heard it on talk radio, TV, at the bar) yet why do some bikers refuse to wear helmets?
On Kyoto, we engineers can do ANYTHING, but we need to eat and thus money needs to be avaiable for us to design environmental systems and such. Should engineers give the order to people to destroy their automobiles? Again, the arguments against pollution have been publically made (NB: cranks like Paul Erlich are still listened too) yet "the people" have voted with their wallets for bigger SUVs.
On Land Mines and weapons issues: War bad, peace good. OK, fine, but men fight, it's in our genes to fight and hate and kill, etc. Land mines, from a tactical standpoint are excellent weapons - REALLY. Mapping mine fields, de-mining places like Cambodia and other places is very costly, though. Too bad, unlike US-made land mines, most of those land mines don't deactivate after 14 days or somesuch. Human history is a history of wars; what makes the engineers any more qualified to force their terms of peace than, say, lawyers, judges or priests? Instead of an oligarchy of philosopher-kings, the world should adopt "Doc" Smith's Lensman's government of technocrat-engineer-kings? Jimmy Carter, an engineer - or pretty darn close - was awarded the Nobel and it wasn't because of his training in nuclear physics; though his Habitat for Humanity sure built a lot of houses. Then again, a lot of Nobels went to folks who helped develop atom bombs and on top of that the prize is named for the man who perfected explosives in the first place. Most of the highly revered names in the history of modern engineering are associated with military works (Coulomb, et al) - is this bad? Is that good?
What make engineers more qualified than Hollywood film stars to comment on human society's ills? I may be able to work calculus problems better than Babs Streisand, but sheesh, she makes a heck of a lot more money than I do and people listen to her.
With all that being said, I do think that an engineer who is so moved by events to speak out, should so do. By all means, write books, send letters, write essays, etc. BUT, once an engineering society, say ASCE, allies itself with a political slant, it's not serving the engineering profession.