In an article for The Chronicle of Higher Education Tom Bartlett refers to the application of evolutionary theory to the study of religion, to determine whether it has social benefits. In this connection he says:
Maybe we should stop asking whether God exists and start asking whether it's useful to believe that he does.
Research shows, he goes on to say, that in certain circumstances religious ideas can induce types of behaviour that are good for society. For my own part, I've never thought different. However, here are three observations I would make prompted by what Bartlett says.
(1) The formulation of his that I quote above shows that whether something is useful and whether it is true must be two different things. Unless this were so, we wouldn't be able sensibly to say, for example: even though p isn't true, it's useful for someone or other to think it's true. If usefulness were just equivalent to truth, we wouldn't have the necessary distinction here.
(2) If the someone-or-other happens to be me, or you, then I, or you, can't use this distinction between truth and usefulness in order to shore up a belief which is useful while not being true. A person can't intelligibly say, 'I know that p is false, but it's useful for me to think it's true, so I will.'
(3) Even if the someone-or-other isn't oneself, there's a certain tension in holding that, though p is false, it's useful for them (i.e. others) to believe p is true. Approaching things in this way puts those who do so into a potentially manipulative relationship to the others with the putatively false beliefs. If you say, roughly, 'Let them be, with their illusions because those illusions are useful and so I won't challenge them', you're putting others beyond the sphere of rational discourse, as if to say 'This, which I couldn't possibly entertain, is good enough for them'.
That doesn't mean one has to be intolerant of beliefs in others that one takes to be false. We can state our own reasons for thinking something false, while completely respecting the right of such others to make up their own minds - to listen to our reasons and accept or reject them as they see fit. But being tolerant of beliefs one doesn't share is different from encouraging others in beliefs one takes to be false - encouraging them on the grounds that the beliefs are useful for them.