My sister used to volunteer at the RSPCA who have this policy. She'd see rabbits and guinea pigs being bought in who were suffering but because the owners were handing them over they wouldnt be taken in. One time my sister had to turn down a rabbit who was going to be fed to her bfs snake if the rescue didn't take it. This system is more promoting animal cruelty it as people are more likely to dump, abuse or dispose of pets as they wont be taken by a rescue.
well if they were dumped or abused then they'd end up in a rescue anyway.
Let me put it another way...
Most of you refuse point blank to go to a pet shop or breeder...however, you're very happy to go along to a rescue and adopt an animal who has come from one of these two places...
Business = supply & demand
the demand is there because those people who got fed up of their animals and dumped them (in whatever way) have been rehomed by yourselves...which allows them to go out and purchase the newest fad animal available...which results in the supply, and the over breeding of sickly animals.