I have perhaps a slightly different perspective to what's been discussed already
I don't eat meat - never have done, since I was born. My parents had stopped eating meat before I was born (couldn't afford it) so I was never given any meat (they never started eating it again either). And as I've grown up and been able to make my own food choices, I simply have no desire to eat meat; I'm not coming from any standpoint, I have no desire to care whether others eat meat or not, but me personally, the thought of eating dead flesh just doesn't appeal, that's all.
In fact, I tend to refer to myself - if the need arises - as "I don't eat meat" rather than calling myself vegetarian - reason being that I've learned over the years that saying I'm vegetarian seems to make people immediately conclude that I'm some meat-eater-hating zealot who goes out campaigning against abbatoirs. I despise animal cruelty, but as I said above, I really couldn't give a jot whether other people eat meat or not. It's never been a political thing for me.
When faced with the inevitable "Do you eat chicken/fish" questions my usual response is "I don't eat anything with a face".
*
Mr Zebra grew up in a meat-eating household but never really enjoyed red meat, and once we got married he stopped eating it altogether (not, I must point out, because of any insisting from my part, he just quite easily found he could stop eating it without missing it). A few years ago, hilarity ensued when he considered trying fish fingers again - they duly sat at the back of the freezer for many months before we concluded that he really didn't want to try them after all.
I've often found it difficult eating in the presence of meat-eaters - because it wasn't something I was accustomed to in my home-life - we'd all be eating vegetables and pasta, that's pretty much it. So having a meal (for example, with Mr Zebra's family, or with work colleagues at Xmas) is quite difficult for me because I'm just not used to seeing meat that close-up. Turns my stomach slightly, and is one of the times I don't mind my anosmia (lack of sense of smell).
For the most part, I don't like 'vegetarian options' because they invariably contain lots of different ingredients and strong tastes that I don't like. I like plain, simple foods. I grew up on a diet of potatoes, carrots, onions, tomatoes, sprouts (I love brussels sprouts), peas, pasta, soups, etc. Plain foods. The most exotic we ever went to was some HP sauce on the top of the veg. Even now, I hate strong spices (unlike Mr Zebra who loves stir fries, vegetarian chinese things like spring rolls, garlic (again another time when I'm thankful for the anosmia) and the like).
So when faced with vegetarian options that usually consist of (the dreaded) aubergines, courgettes, and other strange things that I can't even recognise, I hate it. Give me mashed potatoes and cheese over anything fancy, any day. I do not like meals in which I can't immediately tell what the ingredients are. I'd never want to eat 'meat substitiute' things - I don't want to eat meat, so why would I want to eat something that tasted of it?
At the moment because of my bowel surgery I'm restricted to plain, soft foods and I really don't mind. I'm only eating mashed potatoes (or baked potatoes) with cheese; soups; a bit of bread or soft rolls; yoghurt; grapes and bananas. And it really doesn't bother me. Mr Zebra was just discussing earlier, how hard he would be finding it on this diet but I'm fine with it (luckily I guess!). The hardest thing has been the soup we tried the other day - 'Spring Vegetable' which we only realised upon serving that it contained - urgh - sweetcorn. I spent ages picking out each piece of sweetcorn so I could eat the rest. Mr Zebra ate the excess sweetcorn.
So there you have it
*Except for those 'smiley face' frozen potato thingies.