Sorry if this is patronising but I have to explain this to my students so I'm going into Lecturer Mode.
Most parenting guides, and most books on adoption, trauma and the like fall under this heading. To use a health analogy, these are like either a well-written book on cooking for diabetics, or the Atkins guide. Some individuals may like both - may swear by both - but medically, one can be pretty harmful. Just because something is in a book does not mean it's right, or harmless, or based on any evidence. I hope you all know the same is true for web pages. All the authors in the links given fall under this heading except one (see below).
When researchers do independent studies (not funded by an organisation with an axe to grind) they need to publish them. They can publish in a book, which could be either a scientific book (mainly intended for scientists), or in a college textbook (though rarely without publishing elsewhere first), or in a self-help book. They can also publish on a web page - but see above about web pages.
They can write in a scientific manner and include a lot of references to other people's work. But you're I'm sure all acutely aware it's really easy to misquote or selectively quote other people's work.
So unless another researcher has reviewed the first researcher's work, without knowing who they were (to avoid personal bias), then anything even well-known scientists write could be a misquote, could be based on no evidence, or could be based on anecdotes - on just one person (see below). Peer reviewed work has found that children do not suffer from a change of caregiver at birth purely due to the change of caregiver. The nice links that antiadoption gave me were in fact none of them peer reviewed. In fact, one of the authors (Bruce Perry) she links to is also quite a well-respected author who's written a lot of peer-reviewed papers. He writes on trauma due to maltreatment and severe neglect, and its effects on behaviour and on the brain. He has done absolutely no work that I'm aware of on separation at birth and placement with a loving replacement caregiver.
I think we're all in agreement that mothers who are trying to decide whether to place their newborn for adoption have not maltreated their child, nor have they neglected them. If the adoptive parents maltreat their child, this is awful, if a birth parent maltreats their child, this is also awful, but not really relevant to the question of whether separation at birth and continuing care by loving replacement carers is traumatic. As I said in my previous post, I've seen no peer reviewed work with evidence that it is.
When one person tells you that blood type eating, propping their legs up, having their bumps read, or regression therapy works for them, you might be a bit sceptical. How do they know they weren't going to get thin/pregnant/sane anyway? The gold standard is to randomly compare different conditions in different groups of people - half in each condition - and see what the outcome is - which group improves more. You can do this with therapies for mental health problems. There is no point in comparing a child on a therapy with themselves before the therapy as children grow, and people get better on their own.
But you can't randomly allocate children to being placed for adoption at birth and not being placed. You can only look at naturally occuring situations. You can look at children who are cared for by relatives and neighbours, not their birth mother. You can look at children whose mother died at birth. You can look at children adopted at birth. And when you have two groups, you can look at what else was different (were the grandparents ill and frail? was the father wrapped up in his new wife? were the adoptive or birth parents unrealistic in their expectations, or overindulgent? was the birth mother a sufferer from mental illness so didn't take care of her health/think she could care for her baby?) and only after you've allowed for that can you conclude that separation at birth hurts children. And there is no evidence that it does.
Remember, boys and girls, if you read it on the web it isn't necessarily true. Hope that didn't shock you too much. Here's a large pinch of salt for you to read both my posts and everything else on the web with.
(An an aside - yes, there is a lot of evidence that adoption is traumatic for the birth mother in particular, though I don't know if anyone's looked at outcomes for the birth father. There is a lot that can be done to help people in this situation - and good and bad practices no doubt exist in a variety of places. A new parent's feelings for a child are usually called bonding rather than attachment, as they operate a bit differently - a lot faster, for a start. Even parents who must give up their child - in some cases, who are legally forced to because they have abused them - bond to their child).