if 300,000 per year die from smoking, that accounts for 1 in 5 deaths overall. quite a high percentage, considering not all of the 5 smoke.
"In addition to cigarette smoking as a cause of cancer in smokers, environmental tobacco smoke (ETS) (also called involuntary or passive smoking) is now recognized as a significant cause of lung cancer in nonsmokers (National Research Council, 1986; DHS, 1987; EPA, 1993)"
from http://rex.nci.nih.gov/NCI_Pub_Interface/raterisk/risks67.html
That statistic is even more troubling. Smokers kill a large number of people who don't even smoke.
...and as far as injecting heroin and contracting HIV, it's just stupidity. clean needles are cheap and legal in most places. getting HIV from injecting is really not different from getting it through unprotected sex, in fact its quite obvious even to moron addicts, that the risk is higher.