I had the same thought, but more as an illustration of why the approval process worked exactly as Apple would like here: they likely want to establish a barrier against whimsical provocative marketing but not against serious app development.
If you're willing to make a serious case for why your app is called "Heroin" they might approve it. If you're clearly doing it to make a point, they have every incentive to censor it.
For the record I'm not a fan of this sort of censorship either.
But I'm guessing their aversion to drug references is more to avoid offending people than to discourage drug use: opiate (and amphetamine) abuse is a pretty serious problem around the world, and a lot of people have lost family or years of their own lives to addiction. Naming an app after something with so much destructive potential---and as a marketing gimmick, no less---might seem a bit insensitive to some of these people.
Again, I'm not saying I agree with this logic, but it's a perspective to be mindful of.
If you're willing to make a serious case for why your app is called "Heroin" they might approve it. If you're clearly doing it to make a point, they have every incentive to censor it.