Jorge,
While I agree with you completely about the ethical aspects of
goading animals into violent confrontation for the amusement or
"sport" of an audience, I think Don's little experiment is far
removed from that scenario.   He is investigating the natural feeding
habits of a species (in spite of the light-hearted manner in which he
is reporting the results).  If you are going to keep an animal in
captivity, you have to provide its natural food.  Even some of those
beautiful aquarium fishes require live food.  The natural food of
molluscivorous cones is molluscs.  If they were not attacking and
killing them in Don's aquarium, they would be attacking and killing
them in the ocean.
Regards,
Paul M.
Rhode Island, USA