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I took it to mean that, in MANUAL mode, your camera should not AUTO anything, least of all the ISO, Aperture, or Shutter speed.
Well, here's the thing- you have two dials, already dedicated to shutter speed and aperture. Assuming you want per-shot control of those two variables, and considering that cameras these days can handle higher-ISOs just fine, it seems reasonable to let the metering system figure out the 'correct' exposure.
Except when it doesn't; in this case, you'd want to be able to tell the camera to shoot brighter or darker than what's metered, and the way to do that is through exposure compensation in manual mode.