No, that's not really true. I've known a few weekend crack- and smack- heads. I guess you could say they were addicted, in the sense that a person who has a binge every few weeks is an alcoholic. BTW, the crackheads had regular jobs in a factory, one was a minor union official. Another casuality of the WOsD is the lack of accurate information about both drugs and their users and abusers - most such studies are grant-driven rather than truth-driven. How much time, how many dollars, have been spent trying to prove that marijuana smoke causes cancer? All they have to show is the claim that the smoke "contains more of the [bad chemicals] than tobacco smoke", ignoring entirely the fact that chewing tobacco causes mouth cancer.
Nicotine is more addictive than most schedule one drugs.
risk of instant death by taking one dose,
Common dosage size is affected by prohibition. This is not a fair means of comparison.
long term damage from consumption,
How much? Cigs cause lung cancer, alcohol causes liver damage.
whether "casual consumption" is possible (I would suggest that heroin is not a drug of choice for the "casual" consumer),
Heroin's non-casual status is due more to the heavier law enforcement scrutiny given it than its addictive properties. Same with cocaine.
and medical use.
How can medical uses be determined if a substance is illegal? There are as yet unknown uses for any number of addictive substances which we may never find out about due to prohibition.
Heroin and cocaine, for example, have absolutely zero medical benefits, can easily kill with a single hit, and the long term damage is enormous.
Neither of these substances will kill with a normal, untainted dose. "Single hit" is a misleading term because it fails to distinguish how large the dose is and how clean the drugs are. Long term damage from these drugs is not significantly different from alcoholism. The fact that people believe they are "worse" is purely due to media hype.