Certainly not all habbits are destructive, you seem to confuse habbit with addiction. Addiction to smoking will give you cancer, you can deny it but after 30-40 years of doing this your lungs will tell you, that consequences are severe no matter what you keep telling yourself :) I lost family members to cancer due to cigareres and they were denying it pretty much till the end.
You got one thing right: accepting that your addiction is destructive.
You got one thing wrong: thinking that self-harm is normal and other people's habits are also destructive. Try to change the cigarette in the morning for a 1 hour walking and you yourself you figure out how wrong you were.
