Why is it considered a soft drug? Well I dont have any exact numbers, but Im gonna assume for most people there experience with pot could be similar to mine:
I smoke 3 days a week, a couple of times in each day, have been doing so for roughly 18months, and I have almost no side-effects.
My short-term memory is noticeable worse, but it has very little impact on my life. It may make me forget the occasional word for a minute or a phone number of a friend I havent dialed up in a long time. Importantly though, it dosent stop me learning new memories, especially if I havent smoked in the last 12hrs prior. I am doing a chemical engineering degree right now, its quite intensive but my marks have only improved since I started smoking (Im not saiyng that pot makes you smart, simply that for me and most others, the affect is quite minimal).
As for addiction... well, unless you have say some weird genetic predisposition to cannabis or absolutely no willpower, I really dont see how you could struggle with addiction. Yeah, sometimes I want to smoke when I shouldnt, but I have craved harder for coffee, lollies and coke (cola) at some point harder than I ever have for weed.
The high is quite soft, and for most people, leaves you very very close to reality. Sure, some people really really really like getting stoned- but nonetheless weed dosent take them far from their own mind. I know for myself atleast, even alcohol can put me further away.
Safety: Yes, if you smoke alot, every single day of your life you have a nice chance of getting cancer or smoking related illness... but comparable to say someone who smokes ciggs with the same level of use?-hell no.
Its also quite socially accepted (well, atleast for mid-20s and below), cheap, easy to obtain, and unofficially de-criminalised (depends on ur state). I could go on.. but at the end of day, your still gonna be the same person if you treat this drug with some respect, which for most people is quite easy.
I intend to keep smoking as I am now for the remainder of my degree and then stop. Looking back I expect the benefits will outweigh the negatives.