be allowed to find out who their biological parents are?

yes

i have friends who have been adopted, and its not like they want their real parents to be their parents, but a lot of it is for medical reasons to trace any heart disease etc in the family tree.

but also just to build that connection of friends first, least in my friends cases.

If the parent says no, then I think the answer should be no. I strongly suspect that giving a child up for adoption is not a choice taken lightly and no matter what the child might feel later on in life, if the parent(s) do not want the child to know them, that must be respected.

i may be wrong here, but arent the medical records open for the (adopted) children to get access to to see if there are any diseases or genetic anomalies to deal with?