Medical field not truthful with us or themselves?

Why is it we are told smoking is very bad for us, but I see many doctors and nurses smoke? When you smoke your whole body is changed, and NOT for the better! Are people in the medical field lying to us and smoking really is good for us, or don't they have the self-discipline to practice what they preach?! I even have seen nurses smoke right outside the building where they just gave my wife chemo! Do the hospitals and Doctors know something about smoking that we don't or do the companies that produce these cancer sticks pay them to keep the public sick?! Talking to most people about quitting is like spitting in the wind, but doctors? Come on!!