I think what most people are trying to say is that rabbits+piggies together is like a dinosaur stepping on you, then realising what its done and saying "oops, sorry! didnt mean to!"
Apparently most accidents dont happen because of aggression between the animals, but because of the strong hindlegs. I mean no bunny has eyes in the back of their head, all it takes is one strong hop and the piggy has been kicked in a sensitive place, causing internal injuries... I think this is where most people here are coming from.