I was a vegetarian for 20 years, initially my reason was that I objected to the way animals are treated in the food industry. There is much suffering, and I decided that I would prefer not to be part of it. In those days everyone always wanted you to explain your reasons, which can be fine, but often they just did it to try and outwit you for some reason. They'd say things like, 'well do you eat eggs then?', and if you said yes, 'aha! but that is cruel too', etc etc. I got very fed up with this, because I have never tried to change someone else's mind about their dietary choices, and did not see why these people felt I was under an obligation to provide a full explanation for mine, and to enter into a philosophical debate about it. I just chose a plan that I felt happy with, and knew that it was right for me, but not necessarily for other people.
As years went by and the quality of meat was very questionable at times, with news of dead animals being fed to other animals, mad cow disease and so on, I felt even more sure that I had made a good choice.
I began eating fish again about year ago. I was severely anaemic and I felt that now I was over 40 I could no longer cope very well without major attention being paid to my diet. I have always said that I declined meat by choice but that I would not hesitate to kill and eat anything if I needed to, if I was starving or if my health demanded it. I consider myself more important than any animal. I never really had much objection to fish-eating in the first place, it is much healthier than meat and I do not believe there is much cruelty involved - there is some but it is not on the scale of animal farming cruelty. I personally do not feel emotionally concerned about fish dying to be eaten, but sometimes feel that way about animals. But the tedious way that people always wanted you to justify these choices 20 years ago meant that to do anything more complicated than just being simply a vegetarian would involve endless tiring defensive conversations with which I could not be arsed. Nowadays things are different, there are many more vegetarians and people with every different kind of dietary choice so one can have individual requirements without so much as raising an eyebrow most of the time.
There is a multitude of reasons why people make the food choices they do - moral, religious, health, to please other members of the family, maybe sometimes people don't like the taste or texture. I don't see that it should be a problem, we can all respect each other's right to eat according to our own conscience and not necessarily to have to be asked to explain our motives to anyone with a different philosophy. Unfortunately, as with most subjects, there will always be people who think their way is the only right way. Some ardent vegetarians are as guilty of this as the folk I knew years ago who thought I needed to justify my choices to them.
I am rarely drawn to discuss my food choices for the reasons I have said. There is also a danger that once you state your reasons other people will feel as if you are preaching at them, and I don't want that. But so many questions have been asked on this thread that I decided to at least give my viewpoint and apologise for the length of this post.
Incidentally, I would not refer to myself as vegetarian now, since I eat fish these days. I simply say that I do not eat meat.