where would you have manned flight start
It's already started but it should never be placed above the science. There is simply too many unknowns and the cost of just keeping the astronaut alive is slowing down the science because of the perceived political advantage. As an example, politicians have sold a manned Mars mission because of all the water there that can be turned into fuel.
How do we turn it into fuel there when we can't do it here?
Even if you could take advantage of Daniel Nocera's electrolysis H2 O2 generator the solar constant at Mars would be a quarter of earth's; at the Martian equator while the water is at the poles.
How do we get the water there when Pioneer hasn't found any yet?
Water in abundance is still out of reach. It's very frustrating that we can detect water but haven't been able to measure what is in it yet.
How do we get the astronaut there and keep the astronaut alive for the two year trip?
The launch weight of a space worthy life support system would require the space construction of the manned flight to Mars. Consider that expense. There would still be the effort of enough energy to get that flight moving toward Mars then there is the stopping; which is just as important. Perhaps stopping is even more expensive because the trip out will require a few swingbys to increase the speed of the craft beyond what rocket engines could provide. That spaceship would require some maneuvering to get it into orbit. More expense and energy for those two events. Then the astronauts would need to get down to the surface and back up. Two more sources of energy and expense. Then there is just staying alive on the surface and having enough food and water to do work. I don't think you would pay for a two year trip out just to take a few pictures, pickup a few rock, take another picture of a foot print, and plant a flag. At this point we haven't even considered the return trip and its unique problems.
These are only some of the problems and considerations that require knowledge and viable solutions. All of these take money to prepare for the unknowns of the enterprise. To be sure there are lots of people who would volunteer but volunteers hardly ever come back alive. In the case of a Mars trip they might not get beyond the moon.
Mad Dog, the expense and guarantees of crew safety could be reduced if the numbers of the unknowns could be reduced. That can't happen if all the finances are diverted from science missions, as is happening now, to a manned space program that addresses problems as they are encountered but not known. You know the expression; look before you leap.
During the first world war air combat was at a stage of knights errant in single combat. 20 years later the more sophisticated planes were still manned by knights errant. All of that was learning the hard way out of necessity. Would they have been better off with an F-22? We have the time, why not plan and learn. Manned spaceflight is not dead in my book and there are plenty of opportunities for manned spaceflight experimentation. But, I don't think that you want all your eggs in that basket. NASA, because of political pressures and appointments at the top, is doing just that; putting all the eggs in one basket. We also know what happens when the perceived political goals are met; cut funding and recriminations about how teachers have failed us and why we can't compete in the world market place. Please, what we learned in the first few years about space was far more valuable than all the integrated circuits, tang, and adult sized diapers.
Anecdote: they used to eject that stuff overboard until they finally learned why the system broke down after two days in orbit; it froze solid at the exit port; it's really cold in space.