The value of freedom sometimes calls for constraint: against selling oneself into slavery, for example. Is there an intellectual analogue of this? We generally value open-mindedness, and a willingness to 'follow the arguments' wherever they may lead. But what if some ideas were so corrupting that to consider them seriously would risk undermining one's future capacity for rational thought? It would then seem that there are some ideas that we must close our minds to, if we truly value open-mindedness (and not just for the present moment). This seems a curious possibility.
Such 'intellectual black holes' might fall into either of two classes:
(1) Psychological traps depend on contingent quirks of human cognitive architecture. These might (in principle) be completely arbitrary: we can imagine a creature whose head explodes if it comes to believe that cows eat grass. More realistically, it seems conceivable that some (even true) beliefs might interact to ill effect with our evolved heuristics, biases, and emotional dispositions.
(2) Rational traps, on the other hand, are general to any rational mind. This makes them more philosophically interesting, insofar as they reveal propositions that are essentially (and not merely contingently) antithetical to rational thought.
Now for the big question: are there any such 'intellectual black holes' -- ideas which, if accepted, would undermine one's rational capacities? (And if so, does that necessarily mean we are justified in believing the "trap proposition" to instead be false?)
Perhaps the most obvious example is epistemic nihilism: the view that there is no such thing as epistemic rationality -- all beliefs and arguments are equally good (or bad), and rational persuasion is impossible. Notice that if someone came to really, truly believe this, then it would be utterly impossible to reason them out of it: they would be incapable of treating anything you said as a reason worthy of consideration. Their mind could only be 'rescued' by some non-rational intervention: brain surgery, perhaps.
What other such cases can you think of?