But there are certain substances in drugs and tobacco that induce addiction. It's a bit different from some random loser who has no life and is addicted to an online forum or whatever; the online forum doesn't per se invite you to become addicted. I get your point but I think addictive substances are slightly different than computer games/sex/MTF/etc.
What I'm seeing with this argument is that there are various stimuli that evokes different level of fun/pleasure/happiness (whatever you want to call it). I believe that, the more "fun" a stimuli is, the more addictive it is. Just so happens that drugs are generally "more pleasurable" than say food perhaps. I believe it's the substance or chemicals (better word to use) in drugs provide that incredible kick of pleasure (not necessarily the addiction). Different levels of addiction is dependent across how "fun" or "pleasurable" something is. The relationship is proportional.