> You're right though that smoking shouldn't be top. Everbody dies of something but we can't save all old people from old age diseases forever.

The CDC disagrees. If you click through the last link in the post above they list in great big bold letters "Smoking is the leading cause of preventable death." The key word being "preventable". You're right in that there is little value in worrying about unpreventable causes of death but, please, don't make the mistake of thinking smoking is by any means unpreventable. Also, it's worth pointing out that smoking including second hand smoking kills people of all ages

That's right, but the negatives are presently having a large impact on society. There is a balance to be struck, but it's something that viewing the raw numbers can obscure.

Non-domestic terrorism seems like a good counter-example, where we have gone too far in an attempt to eliminate it: a huge financial and societal undertaking (e.g., the TSA, the justified mass-surveillance, the increase in public fear) for relatively few deaths.

Smoking causes all sorts of harm besides "old age diseases" the happen to "old people." Smoking related deaths and disease effect all ages including fetuses as well as quality of life.