Because nowdays industrial farming has become too abusive, animals are treated like slaves. Such practice is not acceptable and will inevitably backfire. Unless animals can be treated with love and respect, we shouldn't eat them.
How to become a vegan
In order to become vegetarian, one can do a progressive transition by choosing the easiest (according to one's personal tastes) type of meat (pork, beef, chicken) to remove from one's diet. Only until that type of meat has been removed for good that one can choose another type of meat to remove from one's diet.
It is extremely important to combine vegetable proteins (chickpeas, nuts etc) with cereals (rice, wheat etc), or else they will not be assimilated. Eating brown cereals can be good when eating meat, but I recommend to eat white cereals (such as pastas (which may be enriched with iron)) with vegetarian food in order to slow down metabolism. There are enough liposoluble fibers in legumes and nuts. Of course, this could vary as we all have slightly different digestive systems.
B12 Vitamin is only found in bacterias, so many meat products contain B12. When becoming vegetarian, one must find alternative sources of B12 (in free-run hen eggs, some yogurts etc...)
Alternatives to vegetarism
In the future, there will be huge reserves of wildlife animals. Natural non-abusive hunting is part of the animal's ecosystem and is fully acceptable.