I've seen some very sad situations where things have got out of control. 100s of suffering rabbits and guinea pigs in a garden. Starving and inbreeding, giving birth to lethal babies (blind, deaf and infertile ). The owner had mental health problems, and didn't intend to be cruel. But she couldn't cope, and basically abandoned them to die in their cages, until we rescued them.
It Pisses me off to see people get pets, and get rid of them again quickly. I know some one at my work who's gone through about 5 puppies. She gets them, and talks about them, but when I ask how the puppy is doing, I get "Oh, we got rid of it. It was chewing furniture, biting the kids and pissing everywhere". I don't even know what she means by "got rid of it ", and then she'll get another one a few weeks later, and the whole sorry cycle starts again. :(
I have 1 cat from Cats protection, and 2 rescued guinea pigs. It can be very hard to say no. I definitely wanted a cat, and went looking for one, but I was asked to take on the guinea pigs by someone who had lost interest in them. I didn't really want them, but couldn't say no. I feed them and clean them out, but I don't feel any real love or bond with them.
I'd say that it's better to keep the numbers down if you can, but I could easily end up as a mad cat lady.