It has to do with them pumping your food full of hormones so that it grows faster. If i told you, you can wait and let the animal grow naturally or you can have it now and i can pump it full of chemicals and increase your chances of cancer, the answer should be pretty obvious.
There not being enough animals to keep the supply going should be a sign that we are doing things wrong. If meat was more expensive, people would look to other alternatives. There is something wrong with our society when a burger and fries costs less than a salad.
Im not vegan or vegetarian, but if you watch any documentaries in regards to the meat industry, its pretty gross.