User blog comment:Miskos3/Fairy Tail Chapter 508: Pleasure and Pain, Review/@comment-24784846-20161102033214/@comment-7418318-20161102072729

Maybe the condition is what the targets of the spell think of as sinful, not what Larcade thinks.

Sure Natsu enjoyed beating up people, but for him it was always either harmless fun or justified due to those others threatening or hurting his nakama.

Gray's stripping is something he does unintentional, so he might consider it more of a psychological illness than a sinful action.

Besides that, Natsu, Gray and Juvia were already unconscious before the spell was cast and did we even see them after the casting? Lucy was conscious but again we didn't see her.