Not implementing the fork would be an official no-fork position, enforced on everyone running the client. Implementing the fork gives users the ability to choose.

The default was set pro-fork, but that was clearly the most popular option before the software was released. The real decision was made by the miners, and I think it'd be hard to argue that the miners weren't aware of the issue, or didn't have the technical chops to set the option however they liked.