The question of which profession is most analogous to architecture is an interesting one, and one that occupied quite a lot of time at this summer's AIA/ACSA Cranbrook Institute. So let's pursue it. What other industries have "clients" rather than "customers?"
The word "client" comes from the latin word cliens, meaning follower or dependent. The Online Etymology Dictionary (www.etymonline.com) adds that "The ground sense is of one who leans on another for protection."
So as professionals, we protect our clients. We already know that from the health, safety and welfare components of our work, but architects also protect their clients legally and financially.
The question arises, though, whether we have responsibilities to "protect" those who are not our clients. Let's say we're designing a high school (the building type I know best). The client is the party with the checkbook -- the school district, and its State sponsors. So clearly we're required to protect their interests. But there are also innumerable teachers, students, parents, administrative assistants, and coaches who will inhabit this place. Some clients are good at acting as proxies for their ultimate users, and others are awful at it. And then there's the neighborhood surrounding the school -- we have indirect impacts on their lives, through issues of noise and traffic and fear of teenagers, but we also have a direct impact on their property values, whether positive or negative.
Bickford, I think, might argue that conceiving of design and planning as a client/professional exchange is one of the root causes of the spatial inequality that she describes, because it allows the privileged (those who have money to be a design client) to make decisions that affect many others.
So if a client is "one who leans on another for protection," then who protects all the non-clients?