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.
People with schizophrenia (like me) have a long historical association with tobacco smoking. I'm not using this correlation as an excuse. It's just a fact.
Of all things that I perceive as harmful, cigarettes are the least offensive to me. Even though I know that it will bring me pain.
I used to eat watching stuff. Eventually I recognized it as a bad thing. In my case, it distracted me from the food and whatever I was watching. I ultimately dropped this practice and I enjoy my meals way better.
You can see it as a destructive thing, right? Whether it applies to you or not, I wouldn't know.
When I said all habits are self-destructive, I meant that they are conditioning. It's a little part of you that now is in auto mode.
Of course that my example, cigarettes, is also bad for my health. However, the conditioning is mostly chemical (I think), related to nicotine. It was also a way of saying "yeah, I know smoke bad", and a way to make people think of other potential harmful habits (gossip, drugs, promiscuity, stalking, drinking, cheating, etc) and how these things can go hypocritical very fast.