  Given the fast rise of increasingly autonomous artificial agents and robots,
a key acceptability criterion will be the possible moral implications of their
actions. In particular, intelligent persuasive systems (systems designed to
influence humans via communication) constitute a highly sensitive topic because
of their intrinsically social nature. Still, ethical studies in this area are
rare and tend to focus on the output of the required action. Instead, this work
focuses on the persuasive acts themselves (e.g. "is it morally acceptable that
a machine lies or appeals to the emotions of a person to persuade her, even if
for a good end?"). Exploiting a behavioral approach, based on human assessment
of moral dilemmas -- i.e. without any prior assumption of underlying ethical
theories -- this paper reports on a set of experiments. These experiments
address the type of persuader (human or machine), the strategies adopted
(purely argumentative, appeal to positive emotions, appeal to negative
emotions, lie) and the circumstances. Findings display no differences due to
the agent, mild acceptability for persuasion and reveal that truth-conditional
reasoning (i.e. argument validity) is a significant dimension affecting
subjects' judgment. Some implications for the design of intelligent persuasive
systems are discussed.
