i've been thinking for a while about what diets are defensible. georgia ray has an excellent article in asterisk about which animals and animal products are ethical to eat. the long and short of it is that jellyfish and sessile shellfish are ok because they don't think or feel pain, and dairy is more defensible than eggs because it's less work for a cow to produce milk than for a chicken to produce a egg.

the limitation is that i don't think the problem of food ethics can be resolved at the individual level. i don't eat meat, and i haven't for about ten years, not because i feel it as a moral imperative on the basis of some quantifiable metric of suffering, but because of the well documented horrors of factory farming, for animals as well as for the laborers and general environment. i'm also aware that most barnyard animals i wouldn't be comfortable killing myself. i'd be very unhappy killing a chicken, pig or cow. that said, i don't eat fish either (excluding incidental anchovies or fish sauce in restaurant food, which i don't go out of my way to avoid), and i know from experience that i'm not bothered by killing fish. is it fish's taxonomic distance from me or the fact that i can just let it suffocate so the act of killing feels more passive? ray gets at the issue of insect suffering, something i have no qualms about at all. i love killing bugs. i think personal feelings of dis/comfort with kinds of animal suffering are a poor guide to individual action—or perhaps better said, individual action is the wrong register on which to address the problem.

the problems with animal agriculture are social. they're produced on a level vastly beyond any one individual's capacity to influence, unless said individual is a policymaker or agricultural executive. the harms they produce exist on a mind-boggling scale. i don't think it is morally wrong to kill an animal for food in the abstract, nor am i broadly opposed to the use of animal products. i am opposed to the dominant form of animal agriculture in industrialized countries, though, for four basic reasons:

1. it causes far more animal suffering than is strictly necessary
2. it produces work conditions that are exploitative and dangerous
3. it increases the likelihood of novel pathogens spilling over into human populations (whether viruses, superbugs, or prion disease)
4. industrial agriculture, especially animal agriculture, is a huge contributor to water shortages and global heating

i rank them roughly in ascending order of importance, but any single reason is sufficiently disqualifying. the individual act of eating a vegetarian diet is obviously insufficient to address any one, or to remove the individual from a position of culpability. in turn, using my case. as a vegetarian who eats dairy and eggs (and on occasion, incidentally, fish):

1. i willingly participate in factory farming, even buying "humane" eggs and dairy. i know how permissive the certifications "humane" and "cage free" are.
2. even if i went vegan, plant agriculture is still exploitative and damaging to workers' bodies. farming in north america depends on captive migrant labor. the conditions campesinos work and live in are generally unsafe, unfair, and insulting to human dignity. "family farms" and "co-operative" solutions do not solve this. as hamas publicized with their early hostage releases, israeli kibbutzim are mostly staffed by exploited migrant workers. i've seen first-hand the same is true of many "family farms." unless you get produce exclusively from farms where you know the conditions, or grow everything you eat yourself, you can assume exploitative conditions.
3. eating eggs but not chicken arguably makes me more culpable in the inevitable avian flu pandemic, since laying hens tend to be more tightly packed in conditions highly conducive to the rapid spread of pathogens. simply buying "cage free" eggs offers little plausible deniability, as established above.
4. the broad ecological effects of animal agriculture are similarly not exclusive to it—soil degradation, deforestation, water use, carbon emissions, etc. soy, alfalfa, almonds, and countless other crops are culprits in these ecological catastrophes as well.

with even a cursory awareness of the problems of animal agriculture, it becomes obvious that we are not dealing with an ethical problem to be remedied through individual dietary choices, but an entire sector of production that must be razed and rebuilt as a social necessity.

so why do i remain a vegetarian? it's mostly patchwork, capricious personal preferences. it remains the case that i could not kill a chicken or cow myself without feeling gross about it. beyond this, it's cheaper not to buy meat, and i do not make much money. i'm also jewish, albeit not particularly observant, and vegetarianism makes keeping a kosher kitchen basically automatic. not eating meat lowers the risk of food-borne illness (but of course produce contamination, particularly in leafy greens, happens all the time). ultimately, i'm persuaded that reduction in per capita meat consumption, especially in the united steaks of burgmerica, would mitigate the ecological and epidemiological harms of factory farming by simply reducing its scale, though of course it wouldn't eliminate them, nor is any individual's decision to avoid meat a meaningful contribution to this end. so i do not eat meat, and i have no plans to resume eating meat, but to address the problems with animal agriculture requires systemic solutions to remedy its social harms. ethical appeals to individual dietary choices certainly mean something (they meant enough to me to change my diet, after all), but they will not be sufficient.