I think so. As a birth mom, I think NOT telling a child about their adoption is completely wrong, and I urge any adoptive parent to be truthful with their child. But, I think most aparents who do not tell their children about their adoption do so out of ignorance or fear, not maliciously.
Plus, I think as human beings we all make mistakes.....sometimes big ones, and need to be forgiven. As a birth mom, I feel relinquishing my son to adoption was a huge mistake....but, I allowed it to happen out of fear and ignorance. It took me a long time to forgive myself.
Besides, holding on to anger usually hurts the person who holds that anger the most. Letting go of anger is part of the healing process.
I don't know if I could forgive such a thing. How does an adoptive parent sustain a lie like that every day they are with their child? This did not happen to me, but it happened to a close friend of mine. She always suspected she was adopted and her parents never told her. She was almost 50 when she learned the truth. It completely destroyed her. Her life fell apart and I don't think the a-parents had the right to do that to her.