What is the proper relationship between the software developer and the business customer?

Question

IT professionals are experts who are trusted with the IT assets of a business or organisation. As trusted professionals we have responsibilities that extend beyond things that a non-IT customer can be expected to understand or be aware of. So I think the proper relationship between an IT professional and his internal/external customers is more like that between a doctor and patient than a servant and master. Am I right?

Here's an analogy to think about. A patient insists that his leg needs to be amputated. His doctor disagrees but the patient cannot be persuaded. Should the doctor amputate the leg just to satisfy the patient?

Another analogy. A customer wants a civil engineer to build a bridge to an unsafe design. Even when the engineer explains that it is unsafe the customer doesn't believe him. Should the engineer build the bridge anyway?

I think the right answer in both these analogies is NO. The medical professional and engineering professional are supposed to be in a position of trust and ought to exercise their own judgement, even in the face of patient/customer disapproval. Shouldn't the same apply to IT professionals when the IT professional is qualified to make the decision but his customer is not?