Here's an excerpt:
Many people are under the erroneous assumption that an adoptee's desire to search for their biological family is rooted in some sort of ingratitude towards the sacrifices their adoptive parents have made for them. Others assume that the adoptive parents must have been inadequate as parents to cause their adult child to want to search.
The thing is, an adoptee's desire to search is not about their adoptive parents; it's usually about a longing to understand their own roots, or at least to get some much-needed medical history.
I recommend the whole article, although (at least for me) it was a bit hard to follow the progression of events.