Yes, I believe that the protesters were justified in blocking access to the business district in central Auckland while the TPP was being signed. I believe that the blockade was an act of civic participation. The citizens were voicing their displeasure with the largely secretive trade agreement, the TPP. The protesters against the TPP showed their understanding of what their government was doing and that they were aware enough to demonstrate healthy democratic participation and should be applauded.
However the protesters were also perfectly justified in their massive gathering in central Auckland against the signing of the TPP. A numerous and vocal portion of the population clearly opposed the signing, but enough of the whole (or enough of the influential whole) agreed on its passing, so it is justified thus.
Blocking of roads around central Auckland was incredibly immature of them. If they actually wanted to be taken seriously then they wouldn't perform acts of pure stupidity. Blocking off roads is just being a nuisance to other regular citizens who are just trying to do their own thing. Word filler.
The TPP protesters were not justified in blockading central Auckland. The protesters knowingly blocked traffic, with the unknown consequence of blocking emergency responders. Moving the protest to multiple locations throughout the day increased anxiety within the community and police force. Combining the increased anxiety with reduced emergency access can lead to excessive force and explosive chain reactions on both sides. I don't think it's worth risking lives to shut down a city when alternate means of protest are available.
I think the treatment that the police and the black security officers in Auckland for the TPP talks to be atrocious. Of course the western countries needed a secure place but at the same time, they need to be open to dissention because it has some reason to exist and the TPP is just evil.