Given that price tag, what would be the political backlash against NASA if the JWST fails? Would that be enough to cancel other projects for good?
The price tag, ~$6 billion over 15 years and and expected life of 10 years, it's really not that much money in the grand scheme of government expenses.
We dump $700 billion every year into tanks and planes the military doesn't even want. A one time investment in potentially getting a glimpse into the origins of the universe seems so minuscule in comparison.