it all depends on your personality. if you can get high and be responsible you can probably cope with using in moderation. unfortunately, i imagine a majority of people are not like that. i know several friends that have very addictive personalities and getting into junk would have ruined their lives.
a lot of it depends on how its taken as well. mainlining vs snorting vs smoking are all significantly different experiences, the amount taken as well. one can function when its only a small amount taken, increase the dose and you'll be lying around not being able or wanting to move.
i've tried everything under the moon though and i consider heroin pretty dangerous. i would not advise anyone to try it unless they have a very strong head. it is also one of the most amazing experiences i have ever had. the singer of sublime thought he could jump in and get out when he wanted, he overdosed, quite a sad story.