Why would someone think that Adoption erases a child's identity and replaces it with a fake one?

There is nothing fake about me and my very real family or my very real adoptive son, or the very real love and support me husband and me gives to all of our children. So why then would someone say that adoption erases a child's identity and replaces it with a fake one?
Update: People seem to do whatever they can to bash or talk down about adoptive parents on this forum.
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