I would say that the overall package is intended to deter. The detention is probably not the major part of it. The major aspect is the three years of temporary status, and then the restrictions on wider family sponsorship.
I think it is true that detention in and of itself probably may be off-putting, but may not be a major deterrent to people. But with the package we very much want to remove business opportunities from people smugglers who may see them as enabling people to come to New Zealand.