The thought just crossed my mind -- I wonder whether a vague analogy to how it "should" be is to consider children born with a Caesarian section and those who are born "naturally".
It's a fact that some are born one way and some the other, and most mothers would probably be able to tell you how a given child was born if you asked them, but they nearly never bring it up in conversation unprompted (e.g. introducing someone as "and this is my delivered-by-C-section son") nor treat the children differently -- nor do most other people. (Though I wouldn't be surprised to learn that some people might look down on children who weren't born "properly", or consider the mother or the child to be a second-class person due to the circumstances of their birth.)
And that it could be similar with adoption: whether a child is adopted or not is a verifiable fact, but for most intents and purposes should have no bearing on anything. (I still don't know what people-in-general here think, though -- whether they are open-minded and do think this way or could be brought to easily, or whether my paranoia is at least partly justified.)