If an animal can pass the mirror test, you probably shouldn't eat it. Otherwise fair game, brah
Even the lowest of animals with no concept of self still suffer in death, and arguably that suffering is the same that we feel as humans in pain and death. If you can feel empathy for a fellow human in pain, it's not a huge jump to feel bad for other animals in the same situation.
My major beef with vegetarians/vegans on a moral level is that plants and fungi are alive too. They do not have a central nervous system to let them feel pain as animals do, but a plant is still alive - and it must die so you can live.
This is ignoring the ecological aspect though. If part of your morals include not being wasteful of earth's resources, then plants win 100% of the time. Raising animals for slaughter takes tons of feed and water. Then you have the loss of energy from animals being alive and burning calories their whole life. Going up the food chain, you lose more and more of those calories so that a single animal may live. The closer you are to the bottom of the food chain, the less wasteful you are in your eating habits.
