I think a majority of caffeine users are addicted, given the prevalence of idioms on shirts/mugs/etc like "don't talk to me until I've had my morning coffee," etc. Most coffee drinkers I know feel at the very least tired if they don't have a morning coffee, even if they got enough sleep; that lethargy is a withdrawal symptom from a stimulant.

That being said it's a very socially acceptable addiction, and the withdrawal symptoms are non-dangerous (and unless you drink a lot of coffee daily, mild), so people may not feel it's an "addiction" in the same way they think of e.g. heroin, alcohol, etc.

I agree it shouldn't be illegal, and that mildly addictive substances with safe withdrawal symptoms should be legal (i.e. not opiates, but marijuana, coffee, etc). Alcohol is a weird one! It's obviously horrible for you, addictive if you drink it enough, and the withdrawal symptoms are lethal, but our societies have socialized it enough that few enough people become alcoholics — and enough people want it — that bans are worse than allowing it legally, because the downsides of prohibition are a strong black market + gang/mob activities, whereas the downsides of legal alcohol are less widespread in their badness.