A Sad Day for the New Zealand Internet.
Initially when the idea of the DIA Internet Filter (targeted specifically at Child Pornography) was floated I didn't have too many problems with it; their method of implementation (BGP against the IP, and then content filter for HTTP only) is pretty low-impact and the risk of collateral damage is about as low as you could reasonably expect.
However recent media coverage notes that several ISPs are against the filter - which has been launched, but only with Maxnet and Watchdog (others pending) - and some of the reasons identified are pretty damn reasonable.
We have a Single-Point-of-Failure - a single Denial of Service target - and a blocklist which is hidden from public view, so we're trusting our friends at the DIA's Censorship Shop to 'get it right' and to never, ever add content that extends beyond the filters mandate.
So the questions then are,
Do we want another SPOF situation, and
Do we trust the government not to extend the scope of the filter?
Australia has had its own dramas with content filtering - but theirs is mandatory, and far more wide-reaching. The NZ one is 'not too bad' but I have to admit sharing the concerns raised by Slingshot, and others.
In the end, the simple answer is the best; The only people responsible for web content are its creators and publishers. The win over child porn would be to identify and lock up / castrate those who create the content in the first place, and those who make it available. If you need to then nab folks, go for the consumers (the ones who create the market in the first place) who're actually the ones guilty of handling objectionable material.