http://www.nida.nih.gov/infofacts/heroin.html about 23% of users become dependent. Alcohol has 15% addiction rate, I believe.
Heroin (diacetylmorphine) is merely a cheap and potent painkiller, cheaper than other popular ones like oxycodone. It's used in UK to treat severe pain. It's not the strongest one out there (fentanyl is stronger), nor will it make you addicted instantly.
You will probably get addicted if you have easy access and some recurrent pain issues: psychological or physical. A lot of people start off with prescription pharma, and then as their prescription or money runs out, they are forced to use cheaper street alternatives like h.
Others just like to nod once in a while, and only a small part, I believe, makes heroin their ultimate priority enough, willing to kill their own grandmother for a fix. Unfortunately, those junkies are also the most vocal and noticeable ones.
I mean, heroin is not entirely safe and it's very pleasant and it can be addictive just because it's so fucking nice. But I think a lot of people use the idiotic societal stereotypes to justify their own lack of maturity to handle detox, and right now, with the plethora of unaddictive painkillers, rehab, methadone, suboxone, support groups, antidepressants detoxing is easier than ever.