I'm still inclined to think that I don't have a problem with it, if, in the clear light of day with plenty of time and space to think it over, the rationale still holds water.

Or, to put it in more objective terms: If you get someone to do something by improving their decision-making process, or if you cause someone to do something that is instrumentally rational relative to their values, then it's not manipulation. If you believe that premarital sex is okay and you think you can persuade someone to feel the same way, then that's okay.

Aurini's hypothetical example with Mary doesn't pass this criterion. Aurini didn't really believe that donating to the charity would be a good decision for Mary to make.