The title may seem somewhat flippant, but any patent attorney who deals with inventors off the street will ultimately be told about an invention which will quickly be followed by rolling eyes.
The USPTO gives no guidance on this matter. The MPEP Section 10.23 Misconduct deals with classic ethical and potentially illegal actions by patent practioners. For licensed attorneys who must be familiar with the Rules of Professional Condut (RPC), the material will neither seem surprising or novel.
The old favorites are in these rules:
Nowhere in the rules does it say that "Thou shall not file stupid patents." So is the absence of this statement a go ahead to file stupid patents? The answer, as in most cases of the law is both Yes and No.
A patent attorney is hired to use her knowledge, skills, and abilities to best represent the invention in the application to see that it is patented. In a way, we are "hired guns." If we don't do our best, we open ourselves up to RPC violations and malpractice.
However, if we keep pressing on a patent for a REALLY stupid invention, we are making a living based on the client's belief that there will be value in the patent.
We cannot be recklessly indifferent on whether the statements in the application are true or false (MPEP 10.23 (d)).
As patent attorneys we have the ability (in most cases) to choose our clients. When a client has a stupid idea, we can either take on the case or pass on the case. Eventually, if the invention meets the rules for patentability, someone will file the application (possibly, just the inventor).
We also need to understand that as a patent attorneys, what we might think is stupid, may be the next step in technology that moves civilization forward. (n.b. It probably isn't, but it could be!) If we encouraged the inventors not to file, we can be opening ourselves up to costly malpractice suits if we are wrong. If we file the papers, we are performing the work contracted and meeting the RPC and not violating the USPTO Ethics Rules.
In the end, taking the case or not, is not fundamentally different than deciding whether to take a criminal defense case, or an employment case, or a malpractice case. We are masters of our resources and can decide where and how best to use our time. We act as judges the second a person walks in the office to tell her story, and there is no reason not to treat patents in the same way.
In the end, it comes down to personal choice.