We had a bunny neutered because he started humping anyone who sat next to him. He never forgot that, though - he became so aggressive we could barely clean his cage. I wonder sometimes if it didn't mess with his hormones in some way. All our cats/dogs, and ferrets (when we've had rescues), male goats and horse, are neutered. Everyone's always been fine, but for some reason, that rabbit got really p.o.'d! I'd go along with "if it ain't broke..."