The chief reason given by the government for its refusal to support the Zimbabwe Sporting Sanctions Bill (which would impose sporting sanctions on Zimbabwe and thus give the Black Caps an out from their contract with the ICC) is that such action would violate the human rights of New Zealanders. The New Zealand Bill of Rights Act 1990 affirms the right of freedom of movement - including the right of everyone, regardless of citizenship, to leave New Zealand. The Greens have responded with a legal opinion from one of New Zealand's top law firms, arguing that the bill does not violate those rights.
I've finally got round to reading the opinion, and I agree. The argument really boils down to two questions: whether the right of freedom of movement applies to legal persons such as companies and sports teams, and (if it does) whether the restrictions proposed in the bill is a "reasonable limit" as allowed under s. 5. Their response is "no" and "yes" respectively. While it has never been tested in court, it is generally held that the right to leave New Zealand is the sort of right only applicable to individuals, not to legal entities. People have freedom of movement; companies don't, and the bill only limits the latter. But even if this is wrong, and companies do (somehow) enjoy freedom of movement, they argue that it falls well within the "reasonable limits" clause. Travel bans can be a legitimate means of applying pressure to states which refuse to uphold human rights, and in this case the restriction is very narrow; "it is only travel for certain limited, but high-profile, sporting purposes that is prohibited". No individual is prevented from travelling to Zimbabwe, or even from playing cricket there.
If people still have concerns, then the bill can easily be modifed. One obvious amendment would be to remove all references to "travel" entirely, and redefine "Sporting tours of Zimbabwe" to mean the playing of sport in Zimbabwe by any New Zealand national sporting team. Again, this would not criminalise behaviour by individuals, or prevent a "cavaliers"-style "independent" tour, but instead would make it clear that this is about whether a national team should be "doing business" with Mugabe - something the government has every right to prevent.