Scrooge would probably have welcomed the notion that charitable generosity is misguided. But in the mouse experiment described here, it wasn't because of overpopulation:
"Great care was taken to ensure the mice were taken care of, food and water was unlimited allowing mice to eat or drink whenever they pleased and there was always space and clean bedding available so females could rear young in peace and safety.
"Despite this, Calhoun noticed that after day 315 of the experiment, things started to go wrong. First of all there was a noticeable drop in population growth. While initially the population of mouse heaven had doubled every 55 days, after day 315 it doubled, according to Calhoun’s notes, approximately every 145 days. This made little sense as there was still at this time ample space to house an additional 3000 mice.
"In addition to a drop in population growth, Calhoun also noticed an abrupt change in behaviour in both males and females. Social bonds effectively broke down and male mice, without a reason to defend their territory or food source (since both were plentiful) became dejected, forming cliques that randomly attacked one another for seemingly no reason. Females similarly began abandoning young or even attacking them and slowly but surely, both males and females simply stopped breeding...
"... what’s often lost in Calhoun’s work is what came after, in which he continued to research and tweak environmental variables to try to find ways to keep the mice from going down the extinction path even as the population density grew. And, in fact, he had some success at this, for instance in one case via simply encouraging creativity in certain mice by various means. Giving them a sort of purpose here actually worked, with the “creative” mice continuing to thrive well beyond what would have otherwise been expected from the previous experiments."