High cost of launch prevents economical repair (especially in high orbits), which requires extreme reliability. It also creates incentive for extreme weight reduction. Both these drive up the cost of a satellite. At low launch cost, there's no reason a space telescope should be much more expensive than a terrestrial telescope of the same size.
Do you work in the field of space? I don't mean to be dismissive but claiming that space telescopes cost about the same as terrestrial scopes if you subtract out the launch costs and can maintain them with crews, isn't really consistent with what I've heard from space telescope astronomers.
With sufficiently cheap launch, you get radiation hardening with shielding. The goal is to use off the shelf hardware as much as you can. If things break, that's why we have servicing, just like on terrestrial telescopes.
Ah. So, I should have said this earlier: there's a whole different world of cubesats that are what you're looking for. We could almost certainly help the astro community by funding and launching large fleets of simple scopes that make observing time available to more researchers.
You don't service cubesats, you just learn from your past mistakes and launch more.
The cost of rolling a truck to a terrestrial telescope is several orders of magnitude smaller than the cost of servicing a telescope in space. From that difference flows a greater emphasis on reliability for a space-based scope.
