With many human activities there is an element of choice and an element of inner compulsion. That appears to hold for smokers, in that many people find it pretty easy to avoid becoming smokers or to give it up, while others seem to find it impossible to stop smoking. The same goes for drinking.

The assumption that this does not hold when it comes to sexual behaviour is open to question.

Whether it's a matter of choice or compulsion does not alter how we should behave towards people who differ from us in such matters. For example, even if we think that smoking is an unfortunate compulsion or an unwise choice, that does not give us the right to insult smokers.