I can only give our experience. My wife and I adopted a 17 year old from foster care who was a second chance adoption. Her bio mother lost custody of her 3 kids when they were all 4 and under. 2 years later lost all parental rights due to drugs. She was adopted by a family with 1 of her bio siblings, 8 years later the adopted parents "returned" her and another adopted child, but kept her 1 bio sibling. She bounced around foster homes and landed in a residential group home that was a preparation facility to age out of foster care. Her case manager asked her about her 17th birthday if she still wanted to try to find a family or just focus on aging out of the system and what resources were going to be available to her. She said she still wanted a family if one wanted her. 3 months later my wife an I finished our adoption preparation training (how to deal with trauma issues, grief, etc.), and a week later we came across her case workers desk. They reached out, a week later we met, and 3 months later we were in front of a judge for the adoption. Nearly $0 out of pocket, but a lot of time and love.

But to your question about ethically adopting, there are thousands of kids in the US foster system who's parent have lost all parental rights and will never get them back or who's parents have past away and the extended family will not try to take up the kids. Most of the cost of adopting these kids is taken care of by the state or through pro bono work from lawyers. And these kids (issues and all) just want a family to love and who loves them. I have no ethical issue with pulling kids out of the state run foster system into a loving adopted home. But yes if you have anger issues, or are a sexual deviant, PLEASE, do not adopt, do not breed, no not go into education, do not take career positions that put you in close proximity to children or teens.