Visual interaction usability

Early last year I volunteered to serve on a committee tasked with creating a web site for a local nonprofit group. The committee members included, among others, an architect and a graphic designer. Given my background in human-computer interaction, I was pleased to have a cross section of individuals that could each bring their unique talents to the project. After several initial planning meetings in which we discussed the basic look and feel of the web site, I suggested that we make a simple prototype of the design and recruit representative users to attempt carrying out some typical tasks in order to evaluate the site's usability. Much to my surprise, both the architect and graphic designer were vehemently opposed to this idea. Both felt, for slightly different reasons, that the training, knowledge and experience they possessed was a far better metric of the effectiveness of the design than could be obtained by "asking the opinion" of some uninformed potential users.