Feeder fish are a contoversial topic in the forum at the moment. I personally see no problem with duplicating nature in our own aquariums, and I think it is not clear cut as to whether this is cruel. If it is cruel, then we must also remove parasites, snails, water fleas and even algae for their own protection. A sliding scale on the worth of life does not work. Its hard to criticise feeding fish to fish when we herd animals to eat ourselves.
But to my main point, while I dont see this as neccesarily cruel, people who do see it as cruel may be inadvertently offended by how you describe how the fish are 'consumed'. Having a laugh about it may rub salt into the wounds!!
Nature will always do what it does best, the food pyramid is how the system works, even though we can step in and out of it at will, nature pays no heed.
Happy fishkeeping,
Ken