"judging by some of the latest plane crashes, a complete autopilot may not be that bad of an idea."
Until something[0] goes catastrophically wrong. The FMS on that flight threw so many errors that it couldn't compute landing performance metrics. In other words, because it couldn't handle the sheer number of aircraft system failures, it couldn't tell the pilots if the plane would be able to land on the runway and not overshoot it. The pilots hand to manually select which errors to override in order to have the system run its calculations.