Number of New Zealanders killed by alcohol: over one thousand a year [PDF].
Number of New Zealanders killed by tobacco: 5000 a year.
Number of New Zealanders killed by BZP: none.
This isn't just a question of smaller userbases. According to the Expert Advisory Committee on Drugs, 15% of New Zealanders between the ages of 13 and 45 had used party pills in the last twelve months. That's just over 250,000 people. If BZP was even half as dangerous as alcohol, we'd be seeing dozens of attributable deaths a year. Instead, we see none. A consistent and evidence-based approach would suggest adopting a more relaxed policy for a drug which is demonstrably much, much safer.
Unfortunately, BZP is taken predominantly by young people, who can't afford to buy politicians, and who therefore apparently aren't entitled to consistency.