The argument for partial demining leading to increased harm requires that land that is mined remain completely unused otherwise or be completely demined. As soon as there is any use then reducing the number of mines statistically [and yes maybe simplistically] will be better - which would you rather, walk across a field of 200 mines or 400 mines?
Professionally demined areas are only cleared to a level of about 99.6% according to the thread so the argument for increased risk of harm still works in that case - more risk from mines when walking in a 'completely' demined area than in an area in which mines have never been placed.