The Starship is about changing the approach, not applying state of the art to a changed parameter. Currently there is a limit. After Starship is offered on the market, that limit may significantly change, as its main reason to exist is the high price of the launch services.
> All those payloads cost serious money
Right, but if you, say, are going to send off-the shelf - or, ok, almost off-the-shelf :) - Caterpillar to the Moon, the payload cost suddenly drops. This is exaggerration, of course, but the idea is that payloads may become much - orders of magnitude - cheaper to produce.
Today. Space telescopes are much more expensive than their Earth-bound cousins. In a large part because you can't afford failure. With cheap launches you'll send much cheaper telescopes, which will still do the same science - and they are cheaper because they are not made not to fail with very high probability.
Starships bringing fuel up is a stop-gap.
Yes, this one shot mentality is extremely expensive and limiting.
Blast those probes out there in quantity, and iteratively fix them.
Do you have the same attitudes towards helmets whether you're walking on the street or riding a motorcycle? I'm assuming not, because you understand they are different risk profiles.
When risk profiles differ, so do the mitigation strategies. One of the ways spaceflight manages different risk profiles is by implementing a risk-based approach. For example, NASA classifies their software risk based on probability and severity. When risk is high, they leverage more requirements and more oversight as a way of mitigating the risk to an acceptable level.
What you seem to be insinuating is we should be willing to accept more risk. While I agree in principle, the hard part is getting stakeholders (from astronauts to contractors, administrators, politicians, and taxpayers) to agree. They get a say, too.
Why do you believe this is true? It's entirely possible that there's a massive amount of unmet demand that's only economically feasible at lower price points that SpaceX is beginning to unlock with reusability and economies of scale.
Even SpaceX themselves is a huge customer with Starlink. An extremely low cost of launch not only means that you can put drastically more satellites up, but you can put them in lower orbit where they will have a shorter lifespan, because they decay orbit and burn up exponentially faster, mitigating the risk of Kessler Syndrome. You can also iterate the satellites much faster as technology advances and waste less time making sure that the satellite is 'perfect' because you only have one shot at launching a JWST after 20 years of work.
On that note, why is one Hubble or JWST enough? We probably need hundreds if not thousands of them if we want a sufficient observation coverage to be fully away of all extraterrestrial (asteroids and commets) threats that might be coming our way.