I've heard the reason why they keep us is because each feeds on a certain emotion. Whenever one of the creatures gets hungry, they provoke us into acting out in whatever way will feed them best.

[Marg doesn't know either and she's largely defenseless. she knows how to use a crossbow, but a crossbow isn't exactly discreet.

so the visit with her was just a bonus?]

I see. I think there's someone you should meet, someone who shares our views. His name is Trafalgar Law and he doesn't like the creatures, either. Perhaps if we worked together, we could find out more information?