Here we go again. People who drink alcohol, are NOT the same as smokers. Unless they are a chronic alcoholic, their drinking alcohol will not affect everyone else. With smokers, everyone else has to put up with the STINK and the second hand smoke!!!
As many posters have said, it makes them choke, it stings their eyes, it gets onto their lungs, and they struggle because they have respiratory issues. My DH's father smoked like a fucking chimney around him and his brother, and they both developed respiratory issues from their mid teens.
Many smokers ARE selfish and thoughtless, and they STINK. Their clothes, their home, their car, their breath, and everything they touch! As I said on another thread I cannot ever be friends with a smoker, because I can't go to their home. they can't come into my home, I can't sit in a coffee shop with them, and we can't go in the car together, because they stink! So I just point blank refuse to be around anyone who smokes.
Weirdly, my 2 DC (mid 20s,) have about 25 friends between them - ex school, ex-uni, ex colleagues etc - and not ONE of them smokes. Not one. Seems all of them cannot stand to be around smokers either.
As quite a few posters have said on this thread, and another anti smoker thread today, (by the way that's the only two that I've ever seen on mumsnet,) it's amazing how some people manage to find the money for smokes, but can't find the money for food and essentials for their kids. This isn't me saying this, there are posters on these threads saying that their father did it, or people they know NOW do it. Always have a little sneaky stash of money somewhere for the smokes, but no money for essentials for the family.
I can't believe that we still live in a society where people still have this absolutely foul, disgusting habit. Never mind 'oh, but it's so hard to give up,' people are still continuing to start it. Despite it being horribly expensive, and foul and smelly, and bad for your health, and everyone has known it's bad for your health for at LEAST 50 years! Yet people still start it, and they say 'oh but I just can't give it up!!!' 
@LesterBiggott you seem bizarrely invested in defending smokers. Why is that? As someone said earlier in the thread. maybe people are hitting a raw nerve. I also agree with a pp that there is nothing 'petty' about bashing smokers. They deserve it frankly.