When impaired by psychoactive disassociative GHB/GBL another person commonly also under the influence of said substance (not required in all cases) takes it upon themselves to get touchy feely and they are well aware that it is gRape, so often they will close the door to the room or commit said gRape in the back of a truck, isolation is key to a successful gRape.
gRaping is often committed to obtain sexual gratification where it otherwise wouldn't be on the cards.