Even without Johnnie Flip-Flop's last minute intervention in the repeal debate, there would have been no likelihood of "good parents" being charged with a crime for giving their child a "smack," because public interest has always been an implicit element of any investigation, ad the police have always been entitled to use discretion. Key's clause just makes this explicit, and gae him the excuse to vote for the bill without appearing to support it in its original form - allowing him to make political capital out of it. Not very admirable, or principled.
It will be interesting to see which way Flip-Flop jumps if there is a strong vote in favour of the referendum. Tough by phrasing the question so vaguely, the supporters of child beating may have shot themselves in the foot. A vote in favour of the question is not a demmand for the return of Section 59, but an affirmation of support for the status quo. A smack adminsitered by good parents is not a criminal offence in New Zealand. On the other hand, those who abuse or brutalise their children can't hide behind a defence of "reasonable force," which is obviously a good thing (3).
1 - "Smacking bill referendum to be held," unattributed NZPA article, 22nd of August, 2008. (http://www.nbr.co.nz/article/smacking-bill-referendum-be-held-34307)
2 - "A referendum on smacking," posted by idiot/savant on No Right Turn, 22nd of August, 2008. (http://norightturn.blogspot.com/2008/08/referendum-on-smacking.html)
3 - My previous ramblings on Section 59 can be read here: http://lefthandpalm.blogspot.com/2007/04/just-repeal-section-59-please.html