My two cents: there is hope for reconciliation if the abandoning parent is willing to do the hard work.
Before I was even born, my bio-dad abandoned me. (ETA: I use the term 'abandoned' because she is seriously mentally ill. No one should leave their child with a person like my mother.) In retrospect, I can understand how bad his situation must have felt for him: my mom had gotten pregnant purposely, despite their agreement to wait until they were more financially stable AND she was carrying on an affair while he was away in Vietnam. When he discovered the pregnancy, he was desperate; when he discovered the affair (thanks to the neighbor lady), he was beyond that and in despair. Mom, pregnant with me, took off with her lover and he sort of lost it and became a beach bum on Kauai for a while. (they were in Hawaii).It was really sad, and because he chose not to address the situation at the onset--paying child support and such--when my crazy mother petitioned to have my growing up dad adopt me legally, it was only natural that bio-dad's lawyer told him to let it happen. He did, and deeply regretted it. She'd emotionally blackmailed him into believing that if he played nice, he could have access to me. Not true.
I didn't see my bio-dad again, until I was 14 and needed to find him. I didn't realize I had been adopted, but discovered this when I was nine. My adoptive father is Filipino-- I didn't really notice the differences until around then.At thirteen, I found some letters bio-dad been sending my mother over the years, asking to see me, which gave me the courage to reach out, and since then, my bio-dad has been in my life. It's been a long go-round; we had the adoption reversed when I was in my twenties, and we have done a lot of talking and some counseling. We are pretty good now; I've forgiven him for making an immature mistake, and he is a good man. He does have convictions and lives by them. I really love him and I'm glad I took those first steps, despite the price I had to pay. (Unhinged mother, with her first husband seemingly back from the dead... I don't think she's ever forgiven me for bringing him back into her life, even from afar.)
All this to say that there are a lot of shades of gray regarding abandonment. To my bio-dad's credit, he did a good job of being 'dad' to his two children, my younger sisters. I love him for giving me them. Just as I love my growing-up dad for being my dad when I needed one. My mother just made everything so very hard being who she was that people took extreme actions. Neither one of these men, by the way, will ever pat themselves on the back for being 'great dads' or anything like that. They are both pretty humble. I call both of them "Dad". It's been a long road, but now that I don't have to choose which parent to love, it's much easier.
Lastly: shame the parent, shame the child. Be very careful, for the sake of the kids.