I’ve had a couple of scarily angry outbursts in the last couple of months (not the same as SI, I know, but I think if I got relief from it I would probably have done it, too). Anger and other things weren’t really allowed in childhood, in my case, either. Brother seemed more allowed to be upset, however. I don’t resent him for that, but I do resent the inequality and that it’s led to me having to work out how to deal with my buried anger as an adult.
If a child is angry it isn’t helpful to shut them down or make them try to be happy all the time.