A student of mine is writing a very interesting article about restrictions on sex between medical and quasi-medical professionals (from psychotherapists and doctors to massage therapists and opticians) and patients. But he's looking for a good term to fill in the blank:

"One common argument for restricting sex between psychotherapists and their clients is that the clients often have a diminished ability to ___."

The term would mean something like "make wise decisions," but he'd like something shorter, preferably a single word (even if hyphenated). Of course, the claim isn't that all the rest of us are so good at making wise decisions about sex -- only that psychotherapists' clients tend to be even less able to make such decisions than the rest of us. Nor is the claim that the clients have a diminished ability to make wise decisions about sex with their psychotherapists; rather, it's that the emotional or mental problems that send them to the psychotherapist tend to cause a diminished ability to make wise decisions about sex more generally.

Note also that the question at this point isn't whether the argument is accurate, or whether, even if it's accurate, it justifies the regulations. My student is just looking for a clear yet concise term that can be used to fill in that blank (and can be reused many times later in the article, which is why my student is looking for something concise). If you have some tips for this, please post them in the comments. Thanks!