Some people insist on being vegetarians, and give a variety of reasons.....healthier, should not be killing and eating animals, some sort of religious goal.
Life forms have to eat to survive. There are herbivores and carnivores. All are healthy.
Ocean creatures don't have much chance to be herbivores.
Some life forms are both herbivores and carnivores. Humans are one of those.
Vegetarians are welcome to their choice, but they need to leave everyone else out of their choice.