What are the causes of pet overpopulation?

Emma Asked: What are the causes of pet overpopulation?

Okay, I know most people will respond to this question by saying something like: "because of all the irresponsible, morally repugnant MORONS who don't spay/neuter their pets!!!" But think about it, up until the 1960s, NOBODY spayed/neutered their pets. So for all these thousands and thousands of years, cats and dogs were allowed to be as promiscuous and prolific as they pleased, and seemingly no one ever really considered this to be a problem. I'm sure that stray animals (and their offspring) have been present in every city/town/village since the beginning of civilization, so why has it only been in the last century that we've come consider them a problem?

I remember reading an article about (human) world population where one of the experts explained that the tremendous (human) population growth during the last several centuries was "not because people started multiplying like rabbits, but because they stopped dropping like flies." So is the same true for dogs and cats? Is pet overpopulation largely due to the fact that the average dog or cat's life expectancy is considerably longer than it used to be?

When my mom was growing up, she had dozens and dozens of cats. None of them were fixed (that was practically unheard of) and, except for a couple of times when a tom got into a particularly bad fight, the only time they went to the vet was for their yearly rabies shot. A couple got run over by a car, but on average they would live 5-7 years. She says she never remembers any of them being visibly sick- usually they would just start acting strange and a few days later they would run off (presumably to die).

Now, the idea of not regularly taking your pet to vet seems tantamount to child abuse, and it's not uncommon for dogs and cats to live well into their teens and sometimes even into their twenty's. Obviously improving animals' health is a GOOD thing- I know I love my pets and want them to live for a long time! But at the same time, I can't help but suspect that the real reason so many animals are being euthanized at animal shelters is not because of all the irresponsible pet owners who don't spay/neuter their pets, but because of all the good pet owners (like myself) who vaccinate their pets and do everything they can to give them the best medical care.

I've also been thinking about the animal shelters themselves. When exactly did they come into existence? Now, I'm a HUGE supporter of animal shelters- I've been a volunteer at several and I have tremendous respect for the work they do. But sometimes I wonder if all of the animals (especially the cats) who are there need to be. At the restaurant I used to work at, there was a whole colony of stray cats who lived in the parking lot. They were very skittish so you couldn't get close to them, but they had plenty food from the dumpsters and none of them ever looked sick or emaciated. Also, at the apartments where I live, there are a ton of stray cats. However, most of them are pretty friendly, and a lot of residents feed them. Again, they all appear to be reasonably healthy, happy, and well-fed (some of them are practically fat!).

So should these homeless cats be in an animal shelter? It seems ridiculous that anyone would feel the need to "rescue" one of these cats by taking them to a shelter where they'll spend all of their time in a cage and potentially be killed. I know a lot of people would point out that even if cats seemingly can take care of themselves, the average life expectancy for one living on the street is 2 years. But then I think, well butterflies only live for 2 weeks, so how long are animals supposed to live anyway? When it comes to the quality and quantity of our pets lives, what should be our expectations? My grandparents would think that its absurd that I brush my pets teeth; are my grandchildren going to be taking their pets to the orthodontist to be fitted for braces?