Here's an interesting brief-read:
http://lifeprocessprogram.com/lp-blog/library/the-persistent...Here's a paper about treating opiate addicts with pure heroin and it having positive effects: http://onlinelibrary.wiley.com/doi/10.1111/j.1360-0443.2008....
If you read up pretty much any information about the dangers of heroin, you will see that they are overdose (which you can prevent by using the right amounts), risk when mixed with other drugs (including alcohol), and risk surrounding it (e.g. sharing needles, committing crimes to afford it, etc.) You're still as likely to get addicted, but if you know the dose you're putting into your body you'll probably be fine.
Wikipedia (https://en.wikipedia.org/wiki/Heroin#Adverse_effects) cites "Merck Manual of Home Health Handbook – 2nd edition, 2003, p. 2097" for the following statement: "Like most opioids, unadulterated heroin does not cause many long-term complications other than dependence and constipation." Followed by "...purity levels between 40% and 60%; this variation has led to people suffering from overdoses as a result"
Pure Heroin is actually prescribed as a legal drug in some countries, e.g. the UK: http://patient.info/medicine/diamorphine and once inside your body is almost exactly the same as morphine that is prescribed as a painkiller in most countries. These drugs, when prescribed (and therefore completely pure and dosage known), very rarely cause problems for their users other than tolerance build-up and potential for users to use recreationally without knowing what dose to use.
So stop being rude and go do some Googling yourself, or ask any doctor the next time you go see one / are in a hospital, and they'll tell you the same thing.