The thing with seafood is the fact that they have less developed nervous systems, especially if you eat clams and shrimp, etc., and it's easier to get seafood that's been caught in their natural environment rather than having been farmed. See the Kantian ethic consideration.

yes, there are other ways to get protein, I've been availing myself of them for 18 years. It's possible, but when I went high protein, I cut out a lot of beans, one of my favourite sources previously, and that threw one more piece of complexity into cooking. I live with three carnivores and wanted to at least allow some overlap in our diets.