Yeah.
In the short and middle term there are side effects. There are visible side effects like how physically unfit the smoker usually becomes. Then there are also conditions like bronchitis.
Well ok, I've known some fairly healthy smokers.
The obesity correlation seems to be more a matter of personality type and other personal choices. In fact, as I recall, smoking decreases appetite.
If smoking and obesity are relatively "inconsequential" habits when they shave around 10-18% of your life expectancy away, what might a really bad habit be?
I can think of a few off the top of my head:
1. Binge drinking (very common where I live.) - noticeable and significant braindamage.
2. Hard drugs: heroin, crack cocaine, meth, speed, other street drugs cut with crap. - danger of overdose and dirty needles, bad stuff, wrong potency, and so on.
3. Speeding - very dangerous, especially on poorly maintained government roads. - Road toll.
4. Extreme sports - skiing, basejumping, skateboarding to an extent, others.
5. Fighting or boxing or head injury prone sports. - Same as binge drinking.
Any habit which actively risks the continuation of your life in the short-term, I would class as dangerous. Also any habit which significantly damages your capacity to live in the near or middle term is also dangerous.
Again, I simply don't think that smoking falls into this category. Last I checked it takes fully 40 or 50 years for significant health impacts to actively manifest as a consequence of smoking.