So-called 'altruistic' surrogacy is the thin end of the wedge of commercial surrogacy. You can justify anything if you want something badly enough. If no money changes hands then for me it's still important to consider the other forms of coercion or reasons as to why a woman engages with surrogacy. (For the same sex couple mentioned in the OP it's clear as to why they are going down this route, although adoption has long been available to same sex couples in the U.K.)
For 'evidence' of children effected by being surrogate born I would direct you to studies on genealogical bewilderment, which impacts donor conceived children (and adopted children) born via surrogacy and Jessica Kearns who is surrogate-born and has struggled with it and has been able to speak on this as an adult.
Studies by Susan Golumbok are useful to an extent but the children studied are not yet old enough to be considering starting families themselves and when you are raised and frequently told how much you were wanted etc it might not be that easy to voice your feelings about genealogical bewilderment and wanting to know the woman who gave birth to you.
pubmed.ncbi.nlm.nih.gov/21895360/
Many adults who experience genealogical bewilderment as a child, or as an adult, struggle to speak or explore this, sometimes it's not possible to do so until their parents have passed away. It's very complex and in my view, shouldn't be dismissed. It can become very central to how you feel about yourself and can be emotionally damaging and difficult to come to terms with.
If you knew you were born to a poor woman in Ukraine during the war and grew up in let's say, Ireland, would it be normal and natural to wonder about her and what sort of life she had and what she felt during the time she was pregnant with you? How would it feel if you knew that you were born because someone paid (even just 'expenses') a woman to have you?
Adoption always centres the child, surrogacy - all surrogacy - centres the adults.