It's very easy to go way over top when you love animals.
My wife and I have 17 dogs that were all rescued from the streets. Sick, beaten, starving, disabled, blind, lame.... We try to take in the animals that want help and are in bad condition, but we usually end up with perfectly healthy dogs in the process which we find good homes for. BUT, when we bring these dogs in the first thing we do is get them fixed and get them all of their shots and new tags. These are three of the biggest things that people don't consider when they decide they want to start an impropmtu dog shelter.
They'll go out and bring in evey animal they can find, convinced they're helping the situation, but either lack the funds or the knowledge to make sure they don't get sick and die or, just as bad, start reproducing and creating further problems with unwanted dogs.
Of course, if people were more educated and committed to a pet before they go out and buy/rescue them from a shelter, even this problem would slowly heal itself.