Breathing the smoke and grease from frying is definitely not good for you. That’s one reason kitchens tend to have serious ventilation.
But people accept a certain amount of risk, since everyone needs to eat and cooking is a career for many people. Cooking is nowhere near as dangerous as smoking cigarettes.
Do we have reliable data about the incidence of smoking among cooks and food preparation workers? How does it compare to the general population? Smoking is supposed to affect negatively your ability to recognise taste and smell, which are very important if you work in a kitchen but, at the same time, I too know several people who are in that line of business and are smokers.
You know why? Because all the chefs I know say the same thing - smoking is the only way to get any sort of break while in the kitchen, going outside and standing still doing nothing for 5 minutes is not acceptable, but somehow going out and smoking for 5 minutes is absolutely ok in most kitchens. I know some people who picked up smoking only to have an extra break at work.
On the plus side, I also know someone who bought himself an e-cig and somehow buys "blank"(saline/water filled) cartridges for it, just so he can have a short break but without any side effects of actually smoking.
Honestly, depending on the establishment you work in, your sense of taste and smell don’t matter much as a line cook or a regular prep employee. You are outputting dozens of the same dish repeatedly in the same order with the same ratio of ingredients. More of an assembly line with a series of predetermined steps than a creative expression through food. A batch of soup may be tasted once at the beginning of the shift when it is prepared but it usually isn’t being checked on the fly.
But people accept a certain amount of risk, since everyone needs to eat and cooking is a career for many people. Cooking is nowhere near as dangerous as smoking cigarettes.