The problem with the most poignant examples is that it's impossible to find beliefs that signal low status and/or disreputability in the modern mainstream society, and are also uncontroversially true. The mention of any concrete belief that is, to the best of my knowledge, both true and disreputable will likely lead to a dispute over whether it's really true. Yet, claiming that there are no such beliefs at all is a very strong assertion, especially considering that nobody could deny that this would constitute a historically unprecedented state of affairs.

To avoid getting into such disputes, I'll give only two weaker and (hopefully) uncontroversial examples.

As one example, many people have unrealistic idealized views of some important persons in their lives -- their parents, for example, or significant others. If they subject these views to rational scrutiny, and perhaps also embark on fact-finding missions about these persons' embarrassing past mistakes and personal failings, their new opinions will likely be more accurate, but it may make them much unhappier, and possibly also shatter their relationships, with all sorts of potential awful consequences. This seems like a clear and realistic example where less accurate beliefs are in the best interest of everyone involved.

Or, to take another example, the post mentions people who expend some effort to follow certain forms of religious observance. For many people in various religious and ethnic groups, such behavior produces pleasant feelings of one's own virtuousness, as well as positive signals to others that one is a committed, virtuous, and respectable member of the community, with all sorts of advantages that follow from that. Now, if such a person scrutinizes the beliefs on which this behavior is based, and concludes that they're just superstitious nonsense, they will be forced to choose between the onerous and depressing burden of maintaining a dishonest facade or abandoning their observance and facing awful social consequences. I don't see how this can be possibly seen as beneficial, even though it would mean that their beliefs would become closer to reality.