It's not hard for me to see both sides of the coin. My brother was adopted. It was never a secret, or kept from him. My parents went through a very reputable adoption home, and we had paperwork with a bit of his history, some details about his parents, and the reason(s) they surrendered him. He read it several times growing up. Maybe not keeping it a secret is why he was more content about it. He has never expressed any interest in locating his biological family. His motto is, let sleeping dogs lie.
I have a cousin, a little older than him, that was adopted too. He was NEVER told. His mother always said she would tell him when he got older. I don't know if she did, or not.
I can see how, finding out as an adult, he could easily take the attitude that his life was a lie, and he'd be curious to find his biological family.
I have another cousin that put her daughter up for adoption, many years ago. Several years ago, my cousin posted in one of the location services, and her daughter had too. They met, and have had a good relationship every since then. I know it doesn't always turn out so well though.
I know a woman that was adopted, and located her biological family. She sent them a letter. The birth mom replied that she was glad she had been adopted by a good family, but had no desire to meet, or be reunited, and requested all contact be stopped.
My best friend for many years, she's deceased now, but we discussed her childhood every so often. There were so many things she did not understand about her family. From when she was little, her dad was somewhat mean to her. Both her older sister, and oldest brother contributed to her support. Her oldest brother was killed in the Korean war, so the support stopped from him. Her dad got meaner towards her. Her oldest sister got married, and was sending money to support her, but her sister got cancer, then the support stopped, because of medical bills. Later on, she died. At that point, her father became abusive towards her. Her mother would occasionally intervene, but then he would vent his anger on her, so she did not intervene much. Later on, my friend joined the military. When she returned home, to visit, he demanded she pay him the money she owed him for raising her. At that point, her mother intervened, and he began punching her. My friend tackled her dad, had her mother pack up, and got a place for them to live. Eventually, her mother returned home, and he never hit her again, but my friend never saw, or spoke to her dad again.
Like I said, I had known her for many years, and one night, we were talking, and I asked her if there was a chance that her older sister, or brother could have been her real parent, and the people she thought were her parents, were really her grandparents. She did some digging. She managed to find the hospital record of her live birth, not in her hometown, but in a nearby town. It turned out that her older sister was her mother. She was engaged, and her fiance went into the military. She was pregnant, and he was killed before he came back, and they could get married. Back then, attitudes about out-of-wedlock pregnancies were radically different than now, especially in small towns. She, and her mother went out of town for her to have the baby, then her parents raised it as their own. Maybe the dad was angry because he felt saddled with a child he didn't have the money to raise, and since the father was killed in action, he would not be back to marry the daughter, and raise the child. I suspect that when the daughter finally did get married, he was expecting her to talk to her husband about raising the child, and that never happened. She did send money for the child's care, but when she got sick and the money stopped, he was once again stuck with a child he couldn't afford, and didn't want to raise. No one will ever know, because he was long dead by the time my friend found out anything, and so was any family that might have known anything. It did however, clear up some issues for her.
My adopted daughter was old enough to know she was adopted, and knew her biological mother. She later met her biological father as well. Growing up, she didn't want any contact with her mother. She was in her late 20's, when her mother contacted her, and they did visit a couple times before her mother died of cancer. She messed things up with her biological dad, when she stole from him, for drug money. He wants nothing more to do with her.
Sometimes knowing can work out, but sometimes it opens a can of worms that would be best left closed. All I can say is, in these type situations, tread carefully.