Smokers often argue that it was not until recently that we knew the harm that smoking does. That is nonsense. In the 1950's, children were warned not to smoke because it would "stunt your growth". We knew then that it was harmful. It also makes common sense that putting a burning stick in your mouth and inhaling the smoke is not good for you. This is just one of several of the phony excuses that smokers use for not being able to quit.
Another myth that you don't hear much anymore is that smoking is OK if you don't inhale. This was particularly argued for pipe and cigar smoking. The point is that if you are breathing there is no way to avoid inhaling the poison if you are in the same room or space with it.