It seems to me that the number of false things¹ that it is actually instrumentally useful to believe is much less than the number of false things that someone else would like me to think that it is instrumentally useful to believe in order that they may take advantage of my belief in false things.

In other words, for any belief X, if X is false and some person S wants to convince me that my believing X would be instrumentally useful to me, it is almost certainly the case that ① believing X actually isn't instrumentally useful to me, and indeed ② my believing X would put me at a disadvantage to S.

In other other words, the more you try to convince me that believing false things is good for me, the more I will conclude that you are bad for me.

¹ As opposed to merely inaccurate but usually-good-enough approximations, as found in classical physics or kindergarten hygiene instruction