Honestly I see where you are coming from but at the same time I do think it would not be right to remove his backstory just because not everyone can relate to/deal with trauma in the same way he does. or because people can get triggered.
Everyone deals with trauma differently and as time does not heal all wounds it often does help to process it and find coping mechanisms. Halsin is hundreds of years old and centuries past since the events occurred. He grew up, matured and "healed" from his trauma in the best way he could. But like everyone else he isn't perfect nor is the way he copes with it.
I don't see it as him mocking it or "Enjoying the trauma". But sometimes when traumatic events happen not all of it was bad. People in abusive relationships for example often have some happy memories to look back on. ( conscious or unconsciously) which is often why it is so hard for them to get out of the situation etc But we should not punish these people for having these feelings/memories. when they are discussing their trauma they have all the right to talk about that as well. Sometimes it can be even harder to talk about than the bad memories itself because people will judge them harshly for it. People often can/try to understand the pain but start to invalidate their trauma because it can't be "so bad" If you had "fun" as well. Or even go as far as saying they invalidate others trauma by talking about the fact that not all of it was horrible.
Speaking of the "good" is sometimes also done by people as a way to protect themselves. At times people make it seem less bad than it actually was to avoid shame or questions. But also to comfort themselves. Make themselves belief it wasn't so bad to make them feel better. Not saying that is a good thing to do but it is something that happens a lot so would not be a strange thing to add to a piece of dialog.
On top of that a lot of people deal with trauma the way he does and I am glad it's represented. It doesn't have to be done/discussed perfectly because not all stories and people are perfect. In real life these topics also get dealt with rather poorly at times sadly enough. Larian did a pretty good job of showing a range of different people, similar traumas/stories but different (trauma) responses. How you deal with trauma all depends on who you are, your environment, the help/support you got etc And there is not one right or wrong answer to it.
Many people who go through trauma learn how to talk about it in a "lighthearted" way. Sometimes as coping/as a shield sometimes because they healed enough to be able to do so. But being able to talk about it and heal doesn't mean it hasn't left traces and partially formed you into who you are today.
With SA for example some people become extremely avoidant while others become hyper sexual. Neither of these are necessarily good or bad. It just how one responds to what they went through. Some people even go back and forth between them. Some become exclusively monogamous others can no longer bind themselves. Just because you or I would not make the choices or say the things he says. Doesn't mean it's so horrible it has to be cut from the game. I do however agree that the timing of it is a bit off and rather unfortunate. A little heads up would have been nice and it could have been done at a different time or maybe even in a cut scene like astarions grave scene. (with or without the spice) I do like that they touch upon his backstory and it explains so much about him and his choices. But I do wish we got more of it. Maybe even finding the place in the underdark, finding a book or something to spark the conversation, get context. Being able to know how the story ended, tell him they were dead or something. Just more than we have right now because I agree that it feels rushed and out of the blue.
