I think the set of purposes you're considering is too limited. If you want an accurate comparison then a pie graph might always be a bad idea. But if the truth doesn't make you look good then the fact that a pie graph is bad at giving an accurate impression of the data actually is your purpose, and the pie chart might be the best graph for the job.
That is a very slippery slope. As presenters of information we have a responsibility to provide the most accurate information possible in a way that is directly digestible. This responsibility exists in the face of uncomfortable data.
"The most dangerous untruths are truths moderately distorted." - Georg Lichtenberg
Any chart or graph, no matter how precise or sophisticated, can be used to distort. Oftentimes, people will intentionally bombard their audience with hyper-sophisticated and complex data readouts in order to prove how sophisticated their thinking has been (and, by association, how trustworthy their conclusions must be). Hedge funders have been doing a brilliant job of this for decades now. "Kill 'em with complexity" is a time-honored sales tactic.
Sure, but when someone's doing something sketchy its important to be able to recognize that, rather than thinking they're stupid or confused or acting randomly.
When you're discussing what is, don't be blinded by considerations of what ought to be.
