I also have BPD, most certainly stemming from a horrific childhood, and I really struggled parenting for the first few years. I also agree that every parent wants to shelter their child from pain, so I'd be hesitant to blame the BPD for that.

What was most helpful for me was to remind myself of all the things my parents did to me that I came to resent and to make sure I wasn't doing the same thing to my child. No child should have to go through the things that I did, but I'd never take it back because I learned what kind of parent I NEVER want to be. I make sure every day that I'm not doing what was done to me and that I AM doing what SHOULD have been to/for me. For example, emotions were absolutely forbidden in my household. And oh boy, if you said "I love you" then you were asking for a world of hurt. I've made it a point from day one to always let my child know how much I love him. It actually helped me deal with a lot of my skeletons without realizing that was happening.

A tragic childhood can become kind of a priceless life lesson, if you look at it from a different perspective. You can't go back in time and undo what was done, but you can control whether or not that cycle continues to another generation. Nothing is more powerful than knowing you're changing the family dynamics for the better. Take that mom and dad!