Let's start here: there is a good case for New Zealand to have a high-end convention centre with a large exhibition space, and central Auckland would be the only sensible place in the country to put it. Done right, it would attract inbound travel dollars and provide beneficial infrastructure.
But such convention centres are expensive to build and operating costs are such that it can be difficult to make a purely commercial return on the investment. So it's reasonable to consider a public investment in this kind of infrastructure.
What isn't reasonable, or responsible, is to subvert a conventional tendering process in favour of some deal-of-the-century hatched over dinner by the Prime Minister and his senior officials. To trade off legislation intended to protect the vulnerable as a form of corporate welfare. To offer up the assets of a Crown-owned company without even notifying its board. And eventually to falsely claim that a highly critical report by the office of the auditor-general has "totally vindicated" you.
All this becomes especially unreasonable and irresponsible when it transpires that the taxpayer is now in the hole for as much as $130 million on the project. The upshot being that we will end up making a substantial public investment after all, but without the benefits, protections or stakeholder rights that would have been established in a conventionally transparent negotiation process. The taxpayer is effectively over a barrel to a gambling company.
The polite word for ministers and officials who contrive such a situation is "muppets".