Offredalba, IME social workers generally advise against name-changing for two reasons. First is that, generally speaking, it is good advice (and most children are adopted at an age when they know their name). Second, because inevitably on prep course you get given general advice, not advice tailored to your particular situation.
Sometimes, frankly, the social worker simply doesn't think through the situation carefully enough. In my case, we adopted a child intending to keep her name intact, except for regularising the spelling (we'll never know whether the bm was trying to be unique, or was simply illiterate, but it simply isn't fair for a small child to have to constantly insist that yes, their name IS spelt that way). As the months ticked past, information kept trickling out about the birth father. Not accepting of the adoption as we had been told, but deeply bitterly angry and distressed. Further, we discovered that this is a man with a big track record of extreme violence. The social worker kept saying ooh, I bet he's got criminal contacts EVERYWHERE, you'd better watch your back (stupid, stupid woman). This was AFTER he had been told who we are, that we have a birth child etc.
I didn't feel safe. I didn't feel I could keep my children safe. The social worker agreed we weren't safe (without any apology for not having assessed this risk right at the start, before she gave him essential information about us). The only solution she could offer was to change dd's name.
If I'd known all this when we were matched, when dd was a small baby, damn right I would have changed her name. She could have kept her birth name as a middle name, and the risk of her resenting this in later years seems to me a small price to pay for the safety of the entire family.
I do not believe this situation is very unusual. Remember that very few birth parents relinquish their children - most are angry and distressed (understandably) at having their children taken away from them. And remember that a high proportion of birth parents have problems with drugs, alcohol, mental illness, antisocial behaviour. Security risks are a big concern for many if not most adoptive parents.
Like most adoptive parents, I take very seriously my responsibility to keep my child connected with her past. She is only 2, but we talk about her story, I show her photos of her birth parents, she has a lockable box in her room where I keep the things she was given by her birth family. Her name is part of that, but it's not the only way to show respect for a child's birth identity, and sometimes there are more important considerations.