Most people I know believe that heroin (and similar mechanisms) get short-term happiness followed either by long-term unhappiness, or death.

That's the long and short of it, I think. There is no reason not to use heroin to obtain maximum utility (for one's self), if one a.) finds it pleasurable, b.) can afford it, and c.) is able to obtain pure and measured doses. (Or simply uses pharmaceuticals.) The perceived danger of heroin comes from its price and illegality (uncertain dosage + potentially dangerous impurities), which often results in penury, and overdose or illness, for the user.

People also want "real" happiness, by which I presume they mean happiness resulting from actions like painting a picture, and not happiness induced by chemical... which is silly, since the two feelings are produced by the same neurochemistry and functionally identical (i.e., all happiness is ultimately chemical). (The perceived difference may still bother someone enough that they choose a different route, though, especially if they don't realize they can just paint a picture... on heroin.)