@LunaTrap In the case of a family member carrying a child for biological parents - I honestly can't see a child being confused by that, or having issues with it, unless some other factors come into play.
There are many adults now raised by lesbian couples via sperm donors, I think there is evidence how many of them feel- I think for a lot there is interest in their biological origins, I imagine there are some who feel they missed out on having a father figure. I get the impression the majority are happy with their upbringing. I don't know if there are similar studies done on babies born through surrogates in different kinds of families, but my suspicion is that often in these cases it depends on whether the child feels they had a happy upbringing.
My family members who were adopted have no interest in their bio-parents because they feel their parents are their real parents and the biological link doesn't really matter. I know people born in difficult circumstances who think their parents probably should have had an abortion/given the up for adoption. Children will always judge their parents choices if they work out poorly for them.
I think there's two issues with what people are concerned about: one is the right of the child, the other the right of the women involved in surrogacy. I think all children disperse transparency about their biological origins, I'm cautious about saying 'children conceived in x set of circumstances shouldn't exist for their own sake' without evidence it's objectively true.
Regarding the women, I think in the majority of cases commercial surrogacy is damaging, and, possibly akin to prostitution, not a choice everyone can enter willingly. I can't say the same for altruistic surrogacy, and the arguments being made really do seem to take away the agency of all women who make that choice.