If people didn't buy these animals then the trade would end. The pet shop only wants your money. The consequences of irresponsible or impulse buying of pets are that often the animal is dumped, usually un-neutered. The lucky ones may be picked up by a kind person, or rescue centres which are already overwhelmed with the increasing problem. The unlucky ones become strays, prone to being picked up and used for dog-fighting, abuse and torture.
Many strays become victims of serious road accidents.
The feral cat is an offspring of the domesticated cat. It has become feral because it has had no human contact. Colonies of feral cats populate cities and are a major problem for rescue centres to deal with, as well as being a public health risk. Rescue centres are unable to cope with the huge number of unwanted animals they are trying to save. There aren't enough good homes to accommodate the animals, which leads to the devastating and daily destruction of thousands of healthy animals.