This in terms of animal cruelty.
However most things in-between is often people kidding themselves.
I mean do whatever you want but being vegan or vegetarian is nonsense considering humans are omnivores and our gastrointestinal system is made specifically for that.
Since I've lived with many vegetarians in my life so far, I would recommend stocking up on some whey or soy protein powder in the transition phase and possible for longer, also know where you're getting calcium, phosphorous and zinc in your diet. You don't need a lot or supplements, just make sure they are part of your diet somewhere.