This is a horrendous situation for all concerned. I have a visceral reaction to the idea of anyone forcibly removing my child from me, and if it happened, I'm sure that I would fight with every fibre in my body to get her back. This is what has happened to the poor birth parents in this case, and now the adoptive parents must be dreading that the same thing could happen to them. Regardless of the outcome, it's tragic - one set of parents will be desperately unhappy.
Legally, the adoptive parents do now have more rights than the birth parents. Morally, though, I'm not sure that either set of parents has a stronger claim. The child is not the possession of its birth parents or its adoptive parents. He/she does not "belong" to either.
What matters now is whatever is in the best interests of the child, but I'm genuinely not sure what those are or whois in a position to judge.
I presume that the child has now developed a bond with his/her adoptive parents, and that it would therefore be potentially damaging (perhaps devastating) to have that bond broken.
At the same time, I don't know what (if any) the long term effects of adoption are on those who are adopted, or indeed if it is easy to even measure these effects in isolation from the trauma that many adoptees will have experienced prior to adoption or during the transition period immediately afterwards. Does growing up outside of your birth family have an impact on mental health, for example? Is there any research that has looked in to this?
It seems to me that, even if the adoptive parents maintain custody of the child, if that is considered to be the least disruptive option, at the very least the child has an absolute right to know his/her birth parents, to have regular contact with them and to understand the reasons why he/she was removed. It may be very hard all round for both sets of parents to live with this, but I think they should try to make it work for the sake of the child, and the law should support this.
I really feel for all concerned. :(