I'm one of those perpetual non-smokers who can't stand the smell of cigarette smoke and doesn't understand the appeal of smoking, but yes, I think that some people are too hard on smokers.
As far as dating goes, I generally don't think it's too harsh for smoking to be a deal-breaker. In that kind of relationship, there's going to be physical component, specifically in this case, kissing. If the smell/taste of cigarette smoke is a turn-off, then that is going to turn-off the physical attraction.
Now, if a non-smoker feels that they have a strong emotional, mental, intellectual, or spiritual connection with a smoker, and they're going to miss out on what could be a great relationship because they can't overcome the smoking turn-off factor, then that's unfortunate. But, just looking at it realistically, physical attraction is important in dating relationships. Romantic love generally can't exist without physical attraction, and some people, like me, find smoking REALLY unattractive.
As far as friendship goes, the only way I could see it being a deal-breaker is one or both of the people involved are inconsiderate.
I had a great friendship with a smoker in the past because we were both considerate about it. When we first met, he asked me if I smoked, if I had any breathing problems, if I didn't like the smell, etc. On the flipped side, I was considerate of the fact that he occasionally wanted/needed to go outside and smoke, and if we were playing video games or watching a movie I was perfectly willing to put that on hold, go outside, and hang out and talk with him while he smoked. When we went outside, he was careful to stay downwind and make sure that his smoke wasn't blowing on me, and even when it was warm and humid outside, I didn't being out of the A/C because I liked hanging out and talking with him more than staying cool.
On the other hand, a different friend once a had a roommate who had no consideration for where his smoke was. He'd smoke indoors. He never asked if I was bothered by smoke. Sometimes he'd blow his smoke right at me. Not on purpose I think, but just because it didn't once occur to him that it might bother me. I don't think I could be friends with that guy. Not because of the smoking particularly, but because of his inconsiderate nature (that just happened to manifest through his smoking).
In conclusion...
Smoking as a dating deal-breaker? Unfortunate, but understandable. The people involved can probably make it work if they're really willing to do so and compromise, but sharing a kissing mouth with cigarettes, is, to me and many others, just gross.
Smoking as a friendship deal-breaker? That's completely unnecessary. I've experienced first-hand that with a little consideration on both sides, a smoker and a non-smoker can be great friends without either having to give up the kind of air that they choose to inhale.