Having a traumatic childhood means you cannot talk even objectively about your basic foundational experiences without it being "venting", even if you're not actually venting. You just straight up have a huge chunk of your life you can't talk about, full stop, without it being trauma dumping.
And it not being socially acceptable to talk about your own childhood is super alienating. Sometimes people want to know why, and any answer you can give them is going to be off putting.
It's to the point I get irritated when something I said is framed as venting when I'm literally just talking about my life experiences, doing my best to keep emotion out of it.
when I was in high school, I overheard two older students talking about a friend of theirs.
One of them said something like, "it doesn't bother me that [Friend] was in residential mental health treatment, I just wish they wouldn't talk about it ALL the time".
The other replied, "Well, that was all of last year for them. So when they say 'when I was in treatment,' it's like when you say 'last year'."
I try to remember that any time someone says something that sounds Shocking to me. sometimes one person's scary special crisis is another person's last year.