We suffer from alarm fatigue. Targeted alarm of the kind, "Hey! This person is blatantly lying!" is for finding the occasional, rare bad actor. The kind of alarm that needs raising for self-propagating patterns of motivated reasoning is procedural or conceptual. People are mistakenly behaving (in some contexts) as though certain information sources were reliable. This is often part of a compartmentalized pattern; in other contexts, the same people act as though, not only do they personally know, but everybody knows, that those sources are not trustworthy.
To take a simple example, I grew up in a household with a television. That means that, at various times in the day, I was exposed to messages from highly paid expert manipulators trying to persuade me to consume expensive, poor-quality, addictive foods that were likely to damage my mind and body by spiking my blood sugar and lowering my discernment. I watched these messages because they were embedded in other messages exposing me to a sort of story superstimulus with elevated levels of violence and excitement, but mostly devoid of messages from my elders about what sorts of time-tested behaviors are adaptive for the community or individual.
If you try to tell people that TV is bad for kids, they'll maybe feel vaguely guilty, but not really process this as news, because "everybody knows," and go on behaving as though this was fine. If you manage to get through to them that TV ads are Out to Get You, this might get their attention, but only by transmitting an inappropriately concentrated sense of threat - or an unproductive general paranoia.
The usual problem statement in such cases would be how to inform my parents that they should be scared of some particular television commercial or show, with the proper level of urgency, without making a literally false accusation. But the actual problem is that large parts of our world are saturated with this sort of thing - friends have TVs, billboards are everywhere, my parents were already acculturated to some extent by TV, and there are other less immediately obvious unfriendly acculturators like school.
The behavior I'd have wanted my parents to exhibit would probably have started with working out - with friends and community members - and with me and my sister - and first, with each other - a shared model and language for talking about the problem, before we started to do anything about it. Not to blame the proximate target and treat each case as a distinct emergency against a presumed backdrop of safe normality.
The bad news is that vastly powerful cultural forces are deeply unsafe. The good news is that, without any specific defenses against these, or even any clear idea of their shape, we've mostly been doing okay anyway. The bad news is that that's beginning to change.
Stopgap solutions that can be implemented immediately look less like rationing screen time, and more like celebrating a communal Sabbath with clear, traditional standards.
This is why I began Effective Altruism is Self-Recommending with a general account of pyramid and Ponzi schemes - not to single out Effective Altruism as especially nasty, but to explain that such schemes are not only destructive, but extremely common and often legitimated by the authorities. The response I'm trying for is more like Halt, Melt, and Catch Fire.
Cross-posted with minor edits from the comments on Raemon's "Rationalizing" and "Sitting Bolt Upright"