I guarantee you it's not "alarmist". I have a friend who is in charge of a detox/rehab ward at a hospital. It has 40 beds and she told me just yesterday that at any given time, about a third of the guests are white suburbanite teens and are there due to either heroin or crack.
Remember, these are just the ones who got found out. In her estimation, there are 500 undetected users for every person who ends up in the hospital. The ones she sees either got caught by the cops, were taken to the ER after an overdose, or their parents found out and checked them in.
Heroin use is absolutely growing among teens in white suburbia. They go down to the "bad areas" of town to pick up their drugs so they can play gangsta for ten minutes, and impress their friends with their mastery of H.
Of course, later on they get hooked and drop out, and no one ever sees them again. That's why the suburbanites don't know what's going on, because nothing visible is happening under their noses. The pushers aren't standing outside the Starbucks, their homes aren't being burglarized, their cars aren't being stolen, and there's no gunfire in their streets.