Have you ever wondered what is behind fate? A force that is certainly not human, that is for sure. If this power is not human what can it possibly be? Mostly fairies and gods are the source of our fate. For example, Puck and Oberon in a Midsummer Night's Dream are just a few of the influences behind fate. Since Puck and Oberon are not human their ways on interference are certainly powers of fate. The duo are not human, they work in mysterious ways, and are interfering only for the good of the mortals involved, so it can be stated that they are the forces behind fate.
In order for Puck and Oberon's behavior to be inexcusable upon mortals, they would have to be mortals themselves. Human's lives are determined by fate, but their lives are not in the hands of another human. Since Puck and Oberon are not human themselves, they can be considered forces of fate.
Technically the two fairies are only guiding the humans in their journey through their lives and helping them to make the right choices. To be held accountable for their actions, Puck and Oberon would have to be humans, not forces of fate. Since they are considered forces of fate, they have reason to meddle in the mortals lives. The events that have happened due to Puck and Oberon now can be excused since they were acting as a force of fate.
Puck and Oberon enjoy being concealed from the mortal eye. That way these two can help the characters, but one have to deal with the trying to be told to 'mind your own business' since no one can see them. Never in the movie or the play, did Titania, Hermia, Lysander, Helena, Demetrius, or Bottom know that they were...