I am surprized by what your therapist said. I have definitely heard that DPDR can be caused by trauma but for sure a lot of people have DPDR and don't talk about any past trauma. It can be caused by anxiety and panic attacks themselves and these are not necessarily caused by trauma. DPDR is not very well known by every therapist even if they claim the contrary. For example, I have seen a psychiatrist who was adamant that DPDR existed only as a symptom of another disorder. Yet I read in a book by a specialist of DPDR who has worked for decades on that topic only, that DPDR can definitely be a primary disorder, and then I find many research papers saying the same since almost 20 years ago. But that therapist would say that these were wrong and vice versa. We often go to doctors thinking they know the truth, and thinking that any doctor would give the same answer since they have the same source of knowledge. But this isn't true and especially for psychiatrists or psychologists, and especially for not so well known disorders like DPDR.
In any case, I heard many people say that it is a good thing to go to different therapists to find a good one, and so far it is my experience too. And even a lot of therapist (at least the ones I have seen) say this is a good approach and encourage it. Some therapists were very bad and I am glad I didn't stay with them or think all therapists should be like that. Some gave me really bad advice or even were "toxic" people. I personally hate it when they pretend they know the problem for sure and know the solution and try to convince me they will cure me for sure when actually they are just lacking humility or just want to secure a customer. I don't need to be convinced because I am already there to try their method, but by doing that they just make people fall from a higher place when people find out their method doesn't work. Also, maybe like your therapist, they imply with this that there is only one solution, and when that "solution" doesn't work then people feel hopeless. If they expressed a little more doubt and said things like "this is one thing we can try first..." they would initiate a search for a solution instead of promissing an all or nothing cure.
Another kind of therapist that I hate is the kind of therapist that sees no emotion on your face (because you have DPDR) and concludes that you are not suffering but just "thinking too much" and they just need to tell you that you are ok and go home, it's all "in your head". And I have seen a handful like that. Even one that was actually helping me but thought that if I kept coming back was because I didn't want to accept that I was going well already, and she wanted me to stop therapy..... Some just judge people on their appearance, and even if I say something is causing me suffering they don't believe me. Fortunately some are not like that and do listen to what i am actually saying. So I found it useful so far to see several of them. Because there are many different kinds of therapists.
About harm OCD though, I do think it is possible for some people to live with some of these thoughts, as long as they are not considered as important. I have some regularly and really they are so not bothering me that I have almost never mentioned them to therapists. This last sunday, for example, I was with a friend and her 4 year old daughter that I like very much. I was eating and she was walking next to the table with her back to me, and I imagined that I could use the knife that was in my hand to kill her. There is no way I would ever do something any close to that, but I just had the thought. And it was a very vivid thought, very precise, I had the image of the exact scence, I even had the sound. I won't turn into details but it was very graphic. So it did feel digusting, but not so bothering because I think that brains do produce things that don't make any sense sometimes. Interestingly I have had these thoughts mostly about hurting people I loved. I don't know why I have them, or why people have them, maybe it is because I am afraid of not being good enough with people, maybe it is a lack of confidence in relationships that manifests in a brutal way, or perhaps with her it was the fact that she is so lovely and I don't feel I have the skills to be in charge of an important and vulnerable person (like I am afraid if i hold a baby because it's frightening to hold a life in your hands, that could manifest for me as being afraid I would drop it, intentionally or not, but the true meaning would just be that I value this life a lot and at the same time I don't feel confident), but anyway, I am a hundred percent sure I don't find anything attractive in killing people and especially the people I love. I think the thought was there for the opposite reason.
I also regularly have "intrusive thoughts" about touching people when I have a conversation with them, like touching their face, or sometimes touching them in a sexual way (and usually I find myself clenching my fingers, like as an automatic gesture to move on from the thought, which i think is also a very OCD thing). In no way I am going to do such a thing, so for me these thoughts are a minor nuisance, and I don't even try to find a way to prevent them from coming back. Maybe it would be better if they did go away, but not so much that I have spent any time trying to make them leave forever. The harming thoughts are like mental images from a horror movie, but it's just that, a movie. To me it does feel like I have the impulse to do it when they happen, but on some level I think this is not so much an impulse but the fear of impulse itself that is rising. So for me everything tends to show that there is nothing wrong with me. The thoughts probably come because I care for people in the first place, and they can cause discomfort again because I care for people. So personally i just try to be openminded with that weird aspect of what brains can do that doesn't make any sense.
But I don't know how all of this works. Maybe these thoughts could be much more powerful and could frighten me more, or I could have a lot more, I don't know. But I think that just the fact of having these thoughts per se is not necessarily a major nuisance for some people. The fear that is around them is a different story for sure. I had a friend who was afraid of being gay every time he found himself looking at another man, even in a non sexual way. It was probably just OCD. Anyway, fear of being gay is a very typical thought OCD thing, I have heard. People who don't have it can think it isn't important, or some could think it is ridiculous, but for him it was really bad, and it made him miserable, although he knew on some level it didn't make sense. So yes, it can be powerful for sure.
Oh, another thing that I hate with some therapists (sorry this is getting really long... I'm venting now....) is that they just explain to you that your fear is irrational and kind of invalidate it. It's like they were saying "your fear is irrational, now we both know it, so you are wrong for being afraid. You can go home now. You're welcome.", and that's all, they don't help you further. But people are not wrong for being afraid. It's like people who are afraid of spiders, I am sure the majority know that the spiders will not sting them. If you put a huge spider in front of me and promised this kind of spider can not sting, I would still be afraid even if I knew nothing bad could happen. So the fear is there and needs to be treated, not just rejected, invalidated or ridiculed.
Sorry this was really long, I didn't realize I would write that much when I started.