@IsDaGany Kidnapping is a very involved process. It takes a lot of preparation and intention to plan and follow through with a kidnapping, and it's something that's typically done either for immediate personal benefit, or pursuant to cultural norms.
For a while, the Philippines had a pretty big issue with kidnapping for ransom, often with the FBI hostage negotiation team getting involved.
In the realm of cultural motives, it's plausible for people to try to kidnap someone if they think that person is misguided or is acting strongly against social norms.
For example, in societies that practice arranged marriages, if a woman rejects an arranged marriage, it's possible that her own family might kidnap her to force her to marry the person she'd been arranged to wed.
If all the victims of the kidnapping are queer in some way, that could itself be an answer to the motivation of the kidnappers.
What are the deeply-held social values that the Arch Dukes hold? How do queer people go against these deeply-held social values? What good do they think they're accomplishing by kidnapping queer people?
In the united states, there's some history with people being kidnapped and held for extended periods by anti-drug inpatient programs, and also a great deal of history with anti-gay conversion therapy camps doing something similar to queer adults and teenagers.
Often, the families of these queer adults and teenagers believe that this is for the benefit of the individuals, and will aid in the kidnapping.
https://www.reddit.com/r/todayilearned/comments/1r6uye8/til_fred_collins_went_to_visit_his_brother_at_the/