As a vegetarian maybe I can provide some insight to my position.
The reason I consume dairy and eggs is because I think that fundamentally dairy and egg (honey too) production CAN be ethical, whereas I think intentionally killing an animal for food can never be ethical. I'm aware not everyone shares the same opinion - but for me, killing a conscious being for food is not something I want a part in, even if it had a great life before the slaughter.
However I should also note that I carefully select dairy and eggs I consume, only from organic, free range farms that I've researched. I choose the vegan option if I can't be sure of the provenance of the dairy/eggs. In practice I'm vegan most of the time and consume very little dairy/egg.
I do think I might become some form of vegan in the future though, once I've thought about it more.
However, there are a whole bunch of moral inconsistencies in my position. Per calorie, harvesting certain crops probably kills more conscious beings than certain types of fishing. And I'm not sure certain water creatures (bivalves?) even meet the threshold of consciousness, yet I nevertheless would refuse to eat them.
There are a lot of difficult moral issues at the edges that I think most people ignore. For me, the overall goal of my diet is to try and find a balance between providing me adequate nutrition for a healthy life while reducing overall negative moral and ecological impact to everything that isn't me.