Doesn't usually work. There are over a thousand incursions by unmanned aircraft systems along the U.S.-Mexico border each month, per the NORAD commander: https://www.war.gov/News/News-Stories/Article/Article/370778... . They pretty much never result in shutting down air space or launching missiles.

Responding to a single party balloon with a giant laser, thus causing a saner government official to close the airspace because some moron is firing giant lasers into the air, is unusual. Probably not a usable asymmetric attack vector.

I'm equally surprised we don't fend off these rampant goblin threats too!

More pragmatically, such a system would cost multiple millions, and would take years to actually stabilize in a manner that would recover the fictitious costs to shutting down the airports with gaps. (i.e. I'm surprised you so easily bought into the 500k figure)

All because a bunch of idiots lost track of their one balloon, once? The asymmetry is banal. There are cheaper ways that require less planning than that.

If it became a real issue you'd hire someone for $25/hr to patrol with an airsoft gun

This is already a thing in Eastern Europe.

https://www.bbc.com/news/articles/c8655gn84ego

"99 red balloons" starts playing in the background.

I think the general assumption is that the US government is competent enough to know the difference between a party balloon and a real threat, but apparently it is not. At least not under the current admin.