Our fear of risk associated with exploration comes to mind. Why haven't we sent someone to the Moon (again) or Mars? Compared to early sailors, mountaineers,

Our fear of risk associated with exploration comes to mind. Why haven't we sent someone to the Moon (again) or Mars? Compared to early sailors, mountaineers, and polar explorers we seem to have lost the tolerance for dangerous exploration. Otherwise we should have by now sent a person on a (potentially) one-way trip to Mars.