> But many recent examples tend to confirm the unions' argument, including a 2015 crash in Europe. A co-pilot of a Germanwings flight locked the pilot out of the cockpit and deliberately crashed the plane, killing himself and 149 other people, giving credence to the ongoing argument that in an airborne crisis you need two pilots working in concert to save the aircraft

How does that support the argument that two pilots are necessary?

It supports the argument that a determined pilot is going to crash the airplane whether or not there are one or two pilots on the plane!