No, pilots should ensure they're current at navigating without GPS because it can fail, just like pilots practice engine failure procedures and every other emergency / non-normal procedure. That doesn't mean it should be "randomly disabled" for the same reason that you don't test software in production or randomly turn off the engine of the plane. Obviously.
replyWe don't know how it failed. Maybe it displayed their lat/long perfectly but at the wrong altitude. We think of failure as obvious, but it is often nearly impossible to tell unless you are looking for it.
replyAltitude is the least accurate dimension for GPS, and it's also the one dimension that's provided with great accuracy by a really simple mechanical gauge present in every aircraft. There should never be a situation where an incorrect altitude figure from GPS causes a problem.
replyGPS is a 3D measurement.
replyErrors can be along any axis, random, infrequent, drifting, and nonobvious.
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