There is nothing nasty about “demand”. It is a neutral term for requiring someone to do something, or consequences will follow. Replace it with “require” if you dislike it.
Smoking is obviously not a trivial matter.
However - to get back to the actual point, as opposed to semantics - you don’t agree that if you require honesty about smoking, you must display a willingness to listen reasonably when they are honest about that very thing?
To my mind, this is also not a good basis for a relationship, which really ought to be based on mutual trust.
This. Trust isn’t just about “Will you tell me the truth”. It’s also about “Will you treat me with the respect and compassion that I am due as a human being and as someone you profess to love.”
What I was going to say is that if you punish someone for telling you the truth, you should not be surprised if they are less willing to be truthful in the future about the same subject.