Can't balloons be punctured by something less expensive than a stinger? Maybe a drone with a machine gun?
And that leads to the conspiracy that there's someone already has a balloon defense system ready for the inevitable bid.
Using guns against high-altitude balloons is also challenging just from an aerodynamics standpoint. Stall speeds get pretty high up around FL600 even with large wings, so the airplane would have to fly straight at the target with a high closure rate in order to get within effective gun range. This creates some risk of a mid-air collision. Using a guided missile is much safer.
https://www.cbc.ca/news/politics/weather-balloon-canada-chin...
Who knows how many of the thousand rounds actually hit the thing.
I wonder if someone might start filling them with much cheaper hydrogen... what's the cost of all that helium anyway?
Goodyear blimp costs about $100k in helium.
Modern incendiary and explosive rounds fired by fighter jets aren't effective against them becayse they are only triggered by their impact against a hard target, but I'm sure the DoD could come up with a more effective version pretty quickly if it came down to that.