I would like to add both legal and ethical constraints to the term "professional".
When I am dealing with an industry professional (lawyer, doctor, builder, sysadmin, architect, whatever), I expect the advice I get to comply with all the relevant laws and regulations. If my plumber does something to my bathroom that doesn't meet council regulations, then I consider that a very unprofessional job. If I order my builder to do something illegal then I expect a firm "no, I'm not doing that" (hopefully followed by some alternatives that are legal).
I also expect the the professional to comply with industry best practices, including codes of ethics.
Accordingly, any questions or answers on this site that suggest illegal or irregular activities should be closed. Any that contain advice that goes against best practice (for example, disabling UAC) should be closed, unless they offer some very compelling justification for the advice.