I don't need believers. I need professionals instead, that will do their best during the working hours, and implement things as requested, even if they personally think the project itself is totally nonsensical.
However, what I would expect from developers is to be professionals and strive to the high technical quality of implementation, even if they don't believe in the usefulness of the project.
EDIT: Looks like I was not clear about my role. I am not some business owner messing up with the technical decisions and asking developers to "be professionals" and "do what they are asked".
Instead, by "being a professional" I am arguing that we as a technical team need to focus on the technical implementation of the business request, even if we don't believe in the business value. We can tell business if something doesn't make sense to us, but in the end it's their responsibility. We should not push our view of business requirements upon them, as much as we don't want that business push their view of technical implementation to us.