Adoption can be good and necessary -- when it is done to find a home for a child who doesn't have a home.
Remember that foster care and adoption differ in their end goals. Both foster and adoptive parents can build lifelong bonds to the children they care for, but foster parents do not replace and essentially erase the child's ties to their birth kin network. Adoptions legally sever, permanently, the child's links to their birth kin network. In a foster care situation the ultimate goal is to return the child to the original kin network.
Let's clarify that adoption has to be based on the child's right to a mother and father. Any discussion of adult "rights to adopt" is an egregious perversion of adoption and leading the way to human trafficking or at worst, cultural genocide and slavery. This link from Americans for Open Records, an adoption activist groups, clarifies this very nicely:
In cases where children "age out" -- reach the age of emancipation in foster care and never got adopted -- the situation is not nearly as dire as advocates of gay parenting like to claim. Such advocates point to the numbers of children in care who are waiting to be adopted as if these 100,000 kids have no kin in their birth network, aren't in foster homes that are taking care of them, don't have other foster homes that can care for them in the interim, and do not have any heterosexual couples willing to adopt them. All these contentions are so misleading we can call them false.
Most kids in the 100,000 "foster kids waiting to be adopted" figure have living birth kin, but that network is struggling. If they age out, they will most likely still be able to rebuild their connections to the relatives they were born with.
Many of the kids in the system are in foster homes that can take care of them, or they can be transferred to other foster homes or to group homes. If they are already in middle school or older, group homes are not actually the end of the world -- think of boarding school -- especially if the group homes give them the chance to build bonds with other abandoned children.
There are long waiting lists of heterosexual couples who would like to adopt but cannot because of the high costs of the process. In the rare event that there is a kid in foster care for whom no heterosexual adoptive couple is willing and eligible, the solution is to make it easier for families with fewer financial means to adopt, not to open up a market for wealthy gay couples.
When we are talking about homosexual adoption, the difference between foster care and adoption is crucial to keep in mind.
A reasonable position, and one I hold, is that gay couples should be eligible for foster care but not adoption.
Once a gay couple adopts a child legally, the child is removed from his kin network permanently -- something that's controversial when straight couples do it -- and then, even more troublingly, there is no mother and father to replace the kin network that the child is being forced to renounce. "Forced" is an important word here because the children are wards of the system and these decisions are being made for them by society.
If a child has been entrusted to the state or to an adoption system, the system cannot foreclose permanently on the child's chance at having a mother and father. Two mothers or two fathers may be hygienically suitable -- that is to say, two adults of the same sex might be fine when it comes to basics of child care -- but such basics relate to the demands of foster care, not adoption. Adoption is a permanent, lifelong, and coercive change to the child's intergenerational relationships.
You cannot use state force to erase a child's mother and father from the child's life forever, and then replace these with two adults who do not include both a mother and father. To do so, you are forcibly taking something from the child that it is not your right to take, and you aren't restoring to the child the parents the child lost through the initial trauma that led him to the system.
Gay people can be perfectly competent at basic child care, which is why we keep hearing about the social-science consensus that same-sex parenting is okay. The consensus is based on studies that count as "good parenting" basic care of children, like showing them love, bathing them regularly, helping them with their homework, and taking them for pediatric check-ups. For this reason, I support the notion that gay couples can help as foster parents.
But a gay couple by definition is not a legitimate couple for legal adoption. It is a violent act to place a child in a gay couple's home via adoption, because, as I have stated, you are using the coercive power of the state to strip a child of a mom and a dad, then you are not replacing one of those two things the child lost. It's wrong. It would be better for the child to remain in the gay couple's home as a foster child and then age out, and decide as an adult whether to continue honoring the couple as his "parents" or whether to return to a reunited kin network associated with the birth family.
Additional note: It's wrong if the kid is perfectly healthy, and it's wrong if the kid has special needs or a disability. ALL KIDS entrusted to the adoption system should have a chance at having a mom and dad. So those two lesbians in Michigan who used their special-needs children as propaganda to force gay marriage on a state were not only manipulative, they were also doing a disservice to the children they love. It is very possible to hurt people we love--those two lesbians in Michigan being a prime example.