Perusasion or Manipulation of Users

I sometimes face situations in design where there is no clear user motivation to perform a particular task but this task is important for the system to continue. For e.g let us take a hypothetical case. Imagine that Yahoo! is bought by Microsoft and Microsoft decides to integrate all the yahoo id users in to MSN id. So, how would you design the content for users (yahoo loyalist) who are not motivated to do this task? This step is necessary for the system but not for the user. But the system cannot complete this step without the users input.

So when I came across an informative column by Colleen on 10 recipes for persuasive content, it got me thinking that I use a few of these recipes to convince users in following a step that is necessary to complete the process.

Persuasive content is written to motivate the users to do the step that may lead to a better user experience rather than introduce a forced step that the user needs to follow without motivation.  A forced step will lead to a frustrating and poor user experience.

Is this persuasion or manipulation of the user? Another column by Colleen  Winning Content Persuades, Not Manipulates tries to clarify it. I had a discussion with my colleagues (Ripul and Meghna) and we ended with the same conclusion as Colleen that there is thin line between persuasion and manipulation. Some times we may have to slightly manipulate the users to get them do a task along with lot of persuasion.