For years, I've used the metaphor of lifestyle diseases -- obesity, diabetes, heart disease -- to help students understand that seemingly desirable behaviors, when taken to excess, can lead to negative and entirely unintended consequences.  Eat too much, enjoy too much leisure, degrade a system -- your body -- that evolved to prosper under circumstances of scarce food and regular exertion.  As a metaphor, it's served to help students understand that seemingly desirable social behaviors like production, consumption and energy (particularly, fossil energy) utilization can degrade a climate system that served humanity well under circumstances of minimal resource utilization and long-term carbon (coal, oil) sequestration.