As a therapist myself, having practiced in mental health centers and in private practice, I believe that Fellow OCD Sufferer has nailed it! "figuring out if, when, and how much cursing is appropriate is probably part of developing the therapeutic relationship." Absolutely, but mostly for the therapist -- the client should be afforded the safe space to speak in whatever vernacular they choose (short of actually threatening or abusing the therapist or a specific other person). The therapist, however, is BEING PAID to assist the client in their personal goals. That may include an insight-oriented response, "I notice when you talk about your mother-in-law, your voice rises and you swear," or "This situation has REALLY upset you."
"The therapist, more than the client, has a responsibility to gauge whether his or her language, and beliefs about how and when cursing should be used, are helpful or unhelpful to the client and to adjust accordingly." Again, I could not have said it better. This should not include negative judgments or the therapist's personal values, such as the above therapist's statement, "I don't swear and I don't go out with people who do; it's against my religion." That is dripping with value judgment, is overly self-disclosing, and would be experienced as off-putting to any client. It flat states, "I reject others who swear, and I'm above it." IF, as a therapist, I were REALLY uncomfortable with someone's swearing, a reasonable response (of appropriate self-disclosure) would be, "I'm finding myself having difficulty really hearing the intent behind what you are saying because I find the swear words distracting me."
FS: "I am surprised that your therapist revealed what seems like a strong opinion about cursing and her relationship with people who do, as it doesn't seem like that sort of information would be helpful to you considering the circumstances. I can understand why perhaps if a client were being belligerent while cursing, a therapist might consider leaving the situation, but just getting up and leaving doesn't seem like an effective way to deal with disagreements about what level of cursing is appropriate or in any way helpful to the client." Fellow sufferer, you truly have a sophisticated understanding of therapeutic relationship-building. You are right -- it would not be helpful to the client, and is that not what the client is there for? Therapy is meant to be a "helping relationship," and not one that threatens abandonment if the client behaves in a way the therapist experiences as uncomfortable or outside their behavior.
FS: "Cursing can actually be helpful at certain times and to a certain degree." Yes, research even shows this!
FS: "I think that the client should feel free to express his/her beliefs and to not feel that he/she must censor himself/herself extensively." Back to the beginning, this is something that encourage every client to bring up in the very first sessions. A therapist I know asks in her first session, "Have you seen a therapist before?" to uncover a person's previous experiences in therapy, and follows with, "Is there any damage control we need to do?" to uncover anything that did not work well for the client. When she first asked me that, I thought BRAVO!
So, I encourage you to reconsider this therapeutic relationship. If, as Fellow Sufferer says, you feel the need to censor yourself extensively, then consider whether you are going to get YOUR needs met as a PAYING client.