I think this boils down to three concerns. One, that if you can't accept any risk for the crew then you have to do an insane amount of basically non-transferable R&D before going to Mars. Two, you can get more research per dollar from robotic probes instead. And three, you'll contaminate Mars.
One, yes, there will be a lot of risk involved and it is infeasible to mitigate it all in our lifetimes. If we want to go to Mars in our lifetimes, we will need to accept more risk than possibly any manned space mission before. But would it be more risk than faced by, for example, sea explorers hundreds of years ago? Exploration has always been risky. I think it will be sad if we wait hundreds of years to mitigate every possible risk before trying to set foot on Mars. I think there are people out there willing to take on a relatively high level of risk; why deny them the opportunity?
Two, sure, you might have better "ROI" on research using robotic space probes, but be careful with that argument, because if you think about it any further you'll realize that you'll get even better ROI not exploring the solar system at all. If your goal is research for practical purposes then there's plenty of that to do here on and around Earth. If your goal is research for research's sake, then I submit that that's not inherently more virtuous than a goal of human space exploration. I personally prefer the latter and I think the public agrees. And if your goal is research to enable eventually sending humans out there, then we'll learn a whole lot more and faster by actually sending humans as soon as it is remotely feasible.
Three, contamination is inevitable unless you plan to make Mars off limits forever. And if by some chance there is actually life on Mars to contaminate, then I bet there's life elsewhere in the solar system to discover too. I doubt very much that Mars would be our singular chance in the solar system to investigate uncontaminated extraterrestrial life. Also, natural processes have likely already landed bits of Earth on Mars as meteorites, just as bits of Mars have fallen to Earth. If your thesis is that extremophile bacteria that we don't even know about are omnipresent on Earth and could survive on Mars, then they could certainly have contaminated Mars already. And if they did, millions of years of evolution would certainly enable them to outcompete anything we would accidentally introduce from Earth.
One, yes, there will be a lot of risk involved and it is infeasible to mitigate it all in our lifetimes. If we want to go to Mars in our lifetimes, we will need to accept more risk than possibly any manned space mission before. But would it be more risk than faced by, for example, sea explorers hundreds of years ago? Exploration has always been risky. I think it will be sad if we wait hundreds of years to mitigate every possible risk before trying to set foot on Mars. I think there are people out there willing to take on a relatively high level of risk; why deny them the opportunity?
Two, sure, you might have better "ROI" on research using robotic space probes, but be careful with that argument, because if you think about it any further you'll realize that you'll get even better ROI not exploring the solar system at all. If your goal is research for practical purposes then there's plenty of that to do here on and around Earth. If your goal is research for research's sake, then I submit that that's not inherently more virtuous than a goal of human space exploration. I personally prefer the latter and I think the public agrees. And if your goal is research to enable eventually sending humans out there, then we'll learn a whole lot more and faster by actually sending humans as soon as it is remotely feasible.
Three, contamination is inevitable unless you plan to make Mars off limits forever. And if by some chance there is actually life on Mars to contaminate, then I bet there's life elsewhere in the solar system to discover too. I doubt very much that Mars would be our singular chance in the solar system to investigate uncontaminated extraterrestrial life. Also, natural processes have likely already landed bits of Earth on Mars as meteorites, just as bits of Mars have fallen to Earth. If your thesis is that extremophile bacteria that we don't even know about are omnipresent on Earth and could survive on Mars, then they could certainly have contaminated Mars already. And if they did, millions of years of evolution would certainly enable them to outcompete anything we would accidentally introduce from Earth.