This motive behind the removal of emotions is made more clear in "The Age of Steel" where it is done by putting in things that keep them from feeling emotions. In that episode, the deactivation of their emotional inhibitors drives the converted Cybermen insane when they realise what they have become, killing them. This motive may also be applicable to Mondas Cybermen, given their forcible conversion of other lifeforms to Cybermen to maintain their numbers, despite the fact the Mondasians appear to have originally willingly converted themselves as a survival mechanism.