The US isn't a serious nation any longer. The US is increasingly becoming a clown show. The response you'd get if you suggested to consider building two of them - for the reasons you mention - is that people would freak out (two boondoggles, $20 billion in cost, decades of time; that would be the flailing, screeching response).
And rightfully so.
What's the ROI? The hard limit for stuff which is not aimed at producing an improvement in quality of life of taxpayers should be in the dozens of millions , not billions.
Quality of life improvement can be delayed 40 or 50 years, but there should be at least a path.
James Webb Space Telescope has no path, nor does Hubble, nor does the ISS, nor do the Mars missions (private or public), and neither did the Apollo missions as the program was shut down for bankruptcy essentially.
Had the Soviet done the same we'd be laughing at their juvinile understanding of economics, ROI and ROE.
On the other hand NASA mission to collide with an asteroid has a path to save us all , ITER has a path (no pun intended) , mRNA research has a freaking highway at this point, biotech also has a path, even China's bridges to nowhere to pump GDP have a path sometime in the future.
Seems like a good pitch to fund National Labs instead.
National Labs != space.
Unless you have a clear and defined QOL plan then space has proven to be a money sink for the longest time.
The Apollo mission didn't have any clear plan, the Voyager-1-2 missions didn't have any clear plan, Mars missions won't have any clear plan, the ISS didn't have any clear plan, the space shuttle didn't have any clear plan.
Matter of fact it's the opposite of what you claim, if you leave space in the hands of military maybe some QOL trickle down will happen (GPS, Sat communications, ICBMs keeping us safe).
If you leave it in the hands of wide eyed individuals who want to discover exoplanets and clusters which we'll never reach then you'll just throw money down the sink.
Unless we can change our essential nature, I don't see any sustainable path where human civilization stays confined to Earth forever. Those doomsday weapons "keeping us safe" will inevitably be used, especially when it becomes clear that we're utterly trapped.