I was not saying all butterflies should not be kept, but out of every 5, 1 or 2 of them might be a good aquarium candidate. Thus, out of 100 butterflies, I would say maybe 20-40 should actually be considered good aquarium fish.
Longnose and heniochus butterfly are both very easy to keep when kept in the proper system. Heniochus should be kept in schools of at least three. Both species, as well as all butterflies, need to be kept in a tank which water quality is just about ideal, with the nitrates definitely as close to zero as possible.