Bacon - frying bacon - smells far better than it tastes. Mt wife's vego and I try to avoid meat as much as possible, especially at lunchtime. The reasoning behind it is three-fold:
Animal welfare - although one can ensure they buy certified free-range, organic, ethical steaks or lamp chops for preparing at home, with a bacon and eggs at a café, or a ham and cheese roll from a bakery you're usually uncertain. I have a dog, and I love animals - I'd rather minimise their suffering where possible, especially knowing that pigs for example - and in keeping with the thread topic - are smarter than dogs and as smart as three year old humans. One of the worst things I've ever seen was footage from an Indonesian abattoir, of Australian cattle being slaughtered in front of their own siblings - they were lined up in a fenced pathway and one by one, throats slit, and torn apart, while the next in line watched - there was no denying that these creatures knew what was happening, understood the implication, and were terrified of the fact that they were headed for the same fate.
Health - cutting red meat out of your diet is one of the easiest, cheapest things you can do if you're serious about improving your overall well-being and minimising your risk of life-threatening illness. That leaves chicken and fish, right? Well chicken is a lean protein, however not only are they very clever animals, for them to be "harvested" in sufficient numbers to feed us all they must be kept in pretty horrific conditions, living very short, torturous lives. As for fish...
The environment - the amount of energy, water and natural resources that go towards creating, for example, a beef steak go far beyond what we all pay for the average burger; the carbon footprint of a meat-eater is so large that a vegetarian driving a hummer has a smaller impact on the environment than a carnivore who drives a Prius. On fish, we're seeing whole species being wiped out as a result of the large scale fishing practices currently employed to satisfy demand.
Vegans? I can totally agree with them on dairy products - we only have animal milk as a result of depriving cows' young of their feed (which leads to why veal even exists) and I feel guilty every time I buy milk or cheese, but eggs and honey? I can't buy into that - if I owned a chicken, it'd be well looked after - why should her eggs go to waste and not be eaten by me and mine?