Why is there so much shame in adoption?

I have a lot of trouble understanding exactly why adoption is looked upon as something shameful. Not everyone does this, but I some people act really uncomfortable when I talk about my birth daughter, and imply that I should be ashamed of her. People make jokes along the lines of "oh yeah? Well you're adopted!" as if that's some sort of insult. And people shame adoptive parents for infertility, or for 'stealing' a baby. I just don't understand. Can anyone shed some light on this?

I think it's at least partially because historically adoption was treated as a thing shrouded in shame . . . women who became pregnant out of wedlock were often hidden away, and the children they placed for adoption were often kept in dark about even the fact that they were adopted. I think as we continue as a society to be more open and accepting of adoption, these uncomfortable responses will diminish.

I think some of the shame also comes from adoption being seen as a "last resort" to have a family. So many women experience infertility and though they may not see adoption as a "last resort" others do. It shouldn't be seen as a lesser way to grow a family. It's not a cultural norm and people are not properly educated about it (the media certainly doesn't help that). So when there are things in the world that people don't fully understand, it's easy to make these assumptions that are misleading of the true power that adoption can have in families.