Is it really illegal to post an add that you would be willing to adopt a baby due to unwanted children?

I'm not sure of the legalities but I really want to know if anyone knows this because I personally don't see anything wrong with it because people post adds in the newspapers locally here and also all over the internet in different forums where they think that potentially they could reach out to some and it be beneficial to both mother/child and the adoptive parents. Is that so wrong?