The research I'm aware of that points to emotional/psychological difficulties in babies removed from their mother at birth is based on attachment theory. I haven't seen research that says babies born to surrogates have similar difficulties.
I don't have any difficulty though, in accepting that children born through surrogacy or sperm donation will have many questions about their heritage. No matter how well life parents help their children understand how they came to grow up away from birth family, questions will remain. I need to stress that I know many adopted children, now adults, who have strong attachments to their adoptive parents and live happy, fulfilled lives.