Drush cannot disable civicrm debug
The civicrm-disable-debug command isn't defined in civicrm_drush_command().  See line 155:

$items['civicrm-enable-debug'] = array(
  'description' =&gt; "Enable CiviCRM Debugging.",
);


To solve this problem, you can add this below that:

$items['civicrm-disable-debug'] = array(
  'description' =&gt; "Disable CiviCRM Debugging.",
);


This would be an easy item to submit as a pull request so everyone could benefit.