I became vegan to avoid paying for cruelty. Cruelty to me is something like "knowingly inflicting excessive suffering on another being without the need to do so." After doing some research I concluded that there were no animal products I was comfortable consuming i.e. not fitting my definition. The ethics I follow are a combination of personal responsibility and utilitarianism.
Omnivores often make the case that slaughtering animals is no worse than "slaughtering" plants. The veg*n response is typically one of sentience or capacity to feel pain, reasoning that I completely agree with.
However, things get a little bit more complicated, because there are animals without brains that are farmed and killed for food. Namely bivalves ad starfis. Fish have brains, but they are highly brain-stem dominated. The argument that they are complete automatons has, I believe, failed thus far, but there is a lot of evidence to suggest they probably have less capacity for pain than "higher" animals (i.e. further along the evolutionary path that lead to mammals and humans) if any at all. The psychological experience of pain in humans has been tied to highly evolved cerebral regions of the brain.
I don't eat or advocate eating fish, because I don't consider evidence like this strong enough to be satisfactorily convinced. But I do consider it worth taking into account.
The traditional and predominant model of progression from full omnivorism to veganism is typically thought of as something like:
lacto-ovo vegeterian ->
I propose that a slightly different progression is best based on my personal research and internal reasoning. The idea of a progression is that we give up what causes the most suffering, then give up what causes the next to most amount of suffering, etc. This way if someone gets stuck on or satisfied with one of the levels (e.g. vegetarians who don't move on to become vegan) then they've reduced more suffering than someone who stuck with a level using an "inferior" progression. My suggested progression would be something like this:
either vegetarian or brainless-animal-itarian
either vegan or person-who-consumes-no-products-of-animals-with-brains
I base my reasoning on the extreme cruelty involved in the egg and dairy businesses and the fact that they kill plenty of animals in the process of churning out their products. The only difference is the slaughtered or trashed animals are not the product itself.
Fish are arguably subjected to less cruelty and also arguably have less capacity for suffering.
Brainless animals, I'm convinced do not suffer at all. I don't eat them, because I have been at least vegetarian all my life and have no desire to stop. So I consider that ethically equal to non-lacto non-ovo vegetarianism. It's much tidier to just draw the line between animals and plants, which is what I do, but I can't come up with an argument as to my line being superior to the brain line.
I might rank freeganism even higher than veganism depending on how the free food is actually obtained, but that's a seperate issue since it doesn't relate to either of these progressions.
Anticipating your flames, but curious to hear your thoughts.