Why would you not? With >>99% probability, you are never going into space. What difference does it make if your surrogates are robots or other humans?
> assume that any human life is ever not at risk
The problem is not so much the risk per se as the cost of mitigating the risk. Sending humans into space is orders of magnitude more expensive than sending robots into space. Does sending humans produce orders of magnitude more value?
Unmanned missions are absolutely a part of space exploration, but there are a lot of limitations that tend to get glossed over in the "manned vs. unmanned" debate.
They're demonstrably less expensive on a per-mission basis, allowing us to reach further--both financially and technologically--than our manned capability would otherwise permit. They've allowed for a diverse set of scientific missions, including many rather creative ones that would otherwise be impossible for manned crews even if we had a more developed space infrastructure.
But sample-return missions suffer. And those are, arguably, some of the most productive missions space exploration efforts can undertake. In terms of scientific papers published with the SAO/NASA Astrophysics Data System, the number of Apollo/Apollo sample-related papers far outweighs those for other robotic missions. More than that, the rate of publishing continues to outpace them even today, over forty years later.[0][1] We're still seeing a scientific ROI for Apollo. What's really interesting is that a lot of that research has gone in directions that the Apollo mission planners could never have imagined back then. And yes, I recognize that there are some very obvious flaws with this sort of basis for comparison.
By contrast, unmanned sample-return missions are incredibly difficult. There have only been a handful of them: the Soviet Luna program (specifically, Luna 16, 20, and 24), ODC, NASA's Genesis and Stardust, and JAXA's Hayabusa. And while there have been multiple Mars sample return mission proposals in recent years, no one knows how that's going to play out.
All of that aside, the biggest benefit of unmanned exploration in the post-Apollo years has been the simple fact that it's kept space science beyond LEO alive. As much as it pains me, and probably pretty much every single person on HN, major government-backed scientific funding is incredibly difficult to push through. There was never any political will for a massive, long-term push into space going all the way back to Kennedy, LBJ, and especially, Nixon. More than that, even NASA didn't have a post-Apollo plan in place until the very end. After that plan was killed (pretty much DOA), STS--one of the few pieces that was salvaged from it--survived Washington's budgetary battles long enough to reach production mainly because the intelligence community pushed for all sorts of complex and expensive capabilities they pushed onto the shuttle. Almost none of which were ever used.
Basically, manned missions were never really de-prioritized in favor of robotic ones; rather, we just didn't have the capability for extensive manned missions outside of LEO. And there was less than zero political will to replace or supplement STS to provide that capability. We had the shuttle. It looked good. And the electorate liked the pretty pictures, even if they didn't support space spending. There are a lot of reasons why the original retirement dates got pushed back from ~1996 to 2010. STS gets a lot of criticism, but the alternative wasn't another manned system, especially because such a system wouldn't have been able to get the intelligence community onboard. It was more or less STS or nothing.
For the most part, space doesn't seem real to people and politicians alike. Every single politician has a long list of pet projects they believe space-funding could be better spent on "here at home." That logic always seemed pretty dubious to me, precisely because the money was spent here at home. After all, NASA wasn't using stacks of cash as their payloads to spend at the Space Mall. But even in the weeks after Apollo 11, it was common thinking according to opinion polls. Part of me wonders if that sort of thinking would be different today had NASA tried to emphasize the potential long-term returns and the mind-boggling amount of mineral wealth in space. Dropping a few million dollars in precious metals would have gotten some political attention, even if it was nowhere near the cost of the mission that mined them.
In any case, it's pretty much inevitable that we'll see both used alongside one another in the future. Unmanned probes allow us to reach far beyond Mars, while current research into robotics in general will greatly increase the productivity of individual astronauts. They'll be able to do more, and investigate more thoroughly than manned crews could on their own. Plus, robotics will be instrumental for the commercialization of space: they'll help mine redirect and mine asteroids, build up a space-based infrastructure, and more.
