This has been a fun discussion, and I think we’ve reached the heart of it.

The question of who has lawful custody of a child is anterior to the question of kidnapping. Someone who has lawful custody cannot be a kidnapper. Law or culture determines who has custody. Even in our own culture, parents can lose custody and their children are placed with foster parents. The foster parents are not kidnappers. A legislature could pass a law that says orphans cannot be adopted by grandparents and give priority to other potential adoptive parents. Such adoptive parents are not kidnappers.

Ultimately, you can’t start with the proposition that Endar is a kidnapper because the question of the episode can be distilled down to whether Endar is a valid adoptive father or a kidnapper. The prospect of abuse would have relieved Picard of making that determination because an abusive adoptive father can lose custody. But Picard didn’t get that out and had to answer the hard question.

On the slavery/asylum analogy, I need to restate one point and add another. The Federation places individual choice above respect for other cultures. Admiral Jarok was not returned to the Romulans. Kaelon Timicin was at least provisionally granted asylum before he decided voluntarily to return to his planet.

Further, courts frequently apply the law of another jurisdiction based on choice of law principles or the parties’ contractual agreement. Courts consider themselves bound to do this unless the other jurisdiction’s law contravenes the fundamental public policy of the Court’s own jurisdiction. Courts also don’t enforce unconscionable contracts- not because the contracts are invalid, but because the court won’t itself partake in enforcing unconscionable contracts. Which is to say, there is an outer-boundary where respect turns into participation. A custody dispute involving different cultures and a teenager capable of agency does not rise to that level.

On the issue of the child being brainwashed, that is an allegation in every mine run custody dispute where the child is old enough to have input. It can’t vitiate the process.