The cost: 23 years and $10B

The benefit: “JWST’s instruments are designed to make discoveries across the spectrum of astronomy — ranging from the worlds and mini-worlds in our own solar system to alien planets circling distant stars, from the supermassive black hole at the center of our own Milky Way galaxy to the edge of the observable universe.” (https://www.geekwire.com/2021/high-cost-high-risk-high-hopes...)

Extremes on the cost/benefit helped create some extreme emotions, I agree!