The argument I have is mostly applicable to fisheries (i.e. this discussion re: lobsters); it doesn't have much to say about farming.

Lobsters, like much of our seafood, are just plucked up out of the ocean. If we don't eat them, an otter or something does.

As it happens, adult American lobsters have few predators other than man. They're big, well-armored, have immensely powerful claws and live in deep burrows. Juvenile lobsters are vulnerable to ground fish, but an adult lobster is only likely to be eaten by brave seals and humans.

True enough, for now. It seems climate change has created a lobster population boom, though (they love the warmer water), so I would say it's only a matter of time before evolution takes notice of this "free lunch" and adapts some of the neighbouring predators to better get at them.

Whether they suffer more or less when caught vs killed naturally in the ocean, I don't know, but there are other issues with fishing in the ocean, mainly that it is unsustainable.

https://www.scientificamerican.com/article/ocean-fish-number...

Lobsters are basically farmed, at this point.

You can be against factory farming and not be a vegan.

A wolf-eaten chicken also gets courtesy parasites.