The business model known as fast fashion has proved wildly successful. Apparel makers churn out new styles on an ever-shorter cycle, offering them at prices so low — like $5 for a shirt or $20 for jeans — that consumers buy more and more items, sometimes getting only a few wears out of them. But there’s a dark side: The boom in the production of garments has increased carbon emissions and other ecological harms, and generated enormous clothing waste. Some consumers say they would prefer to buy clothing made with less injury to the environment, and brands in the $1.5 …