Sorry, but what does it mean by "open mind", ben?
I don't think a person who has "open mind" are tied to any specific philosophy or religion.
Open-mindedness is mostly about a person who not only receptive to new ideas, but it is really about recognising that other people can freely express their own idea and beliefs, and that other people's ideas or views have values.
Open mind is more about one person's attitude towards others' views or ideas or beliefs. About being able to accept or recognise their ideas, views or beliefs, not simply that of your own personal view or belief.
Having an open mind, is not about being open to your own view or belief, but about being open to other people's view or belief, as if they have as much value as your own.
But clearly you don't feel that way with anyone who disagree with you, with your opinion or your belief.
You attack other people's view, by branding them materialistic, whether that's true or not. Materialism, like atheism, communism are common derogatory terms to label any non-believer that disagree with them, even when these people are not materialists, atheists or communist.
As to the "placebo effect".
That's all about tricking patient into thinking what he is getting, is the real medicine or treatment, when in fact, the medicine or treatment is fake, having no other purpose than using the person's own personal belief to make the patient feel better.
The placebo has nothing to do with materialism or with metaphysics.
My question to you -
Are your religious belief and religious practice merely a "placebo effect" meant to make you "feel better" about yourself, but they are actually "fake" belief and "fake" practice?