Actually in this case Loki was kinda the victim. Yes he was in the form of a mare trying to distract the workhorse, but the way the story reads it seems unlikely that he expected Svaldfari to actually break free and chase him down and manage to impregnate him. Maybe like. One or two of those things. But like, the actual goal was just to make Svaldfari unproductive. Idt Loki's intention was for things to go that far.