And you also can't make a credible business or scientific case for government to finance manned space travel to the Moon or Mars at this point.
Sure I can. It's actually pretty easy to make that argument. But it probably won't happen until one of two things occurs - either there has to be an economic incentive or an existential threat. That's part of what NdGT talks about. We went to the moon to beat the Russians during the Cold War - an existential threat. Once that threat was confirmed to not be an issue anymore we stopped going to the Moon and haven't been back since. We hadn't figured out a way to profit from going there yet and so the government funding went elsewhere. If it looks like China is going to the Moon I guarantee you that the US will find the money to do it too - just in case...
We do need research and exploration, but that can be done most efficiently using robot probes.
Some exploration can be done efficiently with probes. Some cannot be done at all with probes. There are a wide variety of topics for which exploratory probes are quite useless, not the least of which is studying human physiology and life support away from Earth. There is plenty of benefit in probes but the notion that nothing will be gained by sending people is absurd and short sighted. That's like thinking that we can explore the ocean using nothing but satellites and ROVs. They're useful tools but they aren't a replacement for going yourself.