I believe that it absolutely can be justified for precisely the reason you state -- it keeps the experts trained so that they can as a minimum produce things like Europa Clipper. But to me that's just keeping their expertise and the potential that it offers on life support.
Having the technology and infrastructure to produce the things that they are experts at producing but in an unprecedented scale is what we need if we want them to reach their full potential.
It allows them to more rapidly iterate over design ideas by seeing what works and what doesn't. It also allows cheaper destructive testing to work out the bugs instead of waiting a decade to find out if they just wasted billions of dollars and centuries of man years with intrinsically flawed designs.
And ultimately it allows us to build modular self-assembling spacecraft on a scale that we've only dreamed of allowing them to practice their trades in new ways that will unlock new science and knowledge for the human race.
Having the technology and infrastructure to produce the things that they are experts at producing but in an unprecedented scale is what we need if we want them to reach their full potential.
It allows them to more rapidly iterate over design ideas by seeing what works and what doesn't. It also allows cheaper destructive testing to work out the bugs instead of waiting a decade to find out if they just wasted billions of dollars and centuries of man years with intrinsically flawed designs.
And ultimately it allows us to build modular self-assembling spacecraft on a scale that we've only dreamed of allowing them to practice their trades in new ways that will unlock new science and knowledge for the human race.