I believe that belief should be proportioned to credible evidence and demonstrable causality especially where counter-intuitive notions are concerned. Has the evidence been reviewed by a group of peers?
Equally we can deny the reality of the Holocaust or the evidence of global warming. Does the media tell us the truth or is it up to us to read critically and listen critically in order to arrive at a more objective truth of events? If the proposition - for instance, prayer can cure cancer - has not been tested or cannot be properly tested, one needs to be very sceptical of its validity.
And when paraphrasing or quoting, always give credit. In Dante's eyes, liars are sent to hell and truth holds a high standard to life, without truth one must face the consequence of lying.
Use a quote that emphasizes or illustrates the thesis. When carrying out such experiments, one needs to be aware of 'the placebo effect', whereby people often report improvements in health even when no drug has been administered, and 'the Hawthorne effect', whereby people's behaviour changes simply as a response to being observed in an experiment.
Sometimes it is better not to tell the truth. Truth is an intrinsic part of human history and culture.