This sort of reminds me of when you talk about religion. If a non religious person talks to someone who is religious then GENERALLY (and that is a generalisation and not true for all cases) the non religious person can accept that the other person has those religious beliefs, yet the religious person can't possibly accept that the non religious person is not religious.
In this case the vegetarian person can not possibly accept that a meat eater is a meat eater, but a meat eater can accept that the person is a vegetarian.
In some ways, that attitude is actually very narrow minded.
Instead of making people feel bad, or whatever, why not just accept that people have different opinions? You don't have to agree with what they do, but you also don't have to make people feel bad or force your views on them either.