Before I am accused of justifying something that I do, I will clarify that I do not smoke. I agree that smoking a pack a day or more is certainly assur. But when the case against a practice is overstated to the point of being silly, the people who need to hear the message will dismiss it entirely.
“Smoking a single cigarette should also be asur because it can lead to a habit and then an addiction.”
The majority of people who smoke one cigarette do not eventually become addicted to heavy smoking. In the U.S. today most people who smoke, smoke socially or on occasion at rates much lower than a pack a day. People that smoke intermittently also have a much easier time quitting. The facts in that sefer quoted above just aren’t true.
We cannot make up new geizeros in modern times (without a Sanhedrin). A school or even a shul, if it wishes, can make a takana for itself, but that is not binding on Klal Yisrael.
As a practical matter, if we want to protect the lives of our fellow Jews, it would be better to stick to the facts. Say that if someone wants to smoke, they should not do so on a daily basis and when they do smoke, they should smoke only one or two cigarettes.