What if you could prove to other people you are sincere about what you write, or least prove you have sincere and good intentions, even if they aren't exactly the ones you write? We might be able to do that one day with BCIs. Just imagine: some time in the next 15 years, after advanced (way, way, way better than EEG) new forms of BCIs become available and commonplace, and several generations after advanced AI systems for decoding the brain have also become commonplace, people routinely use them on social media when they make a post about some idea they had.
Say, for example, they claim to be interested in the environment. Their brain scan will reveal they have a genuine interest in the subject; show signs of genuine fear and anguish when talking about the effects of global warming; and also show signs they really believe in what they say about how to fix it. What they say is exactly what their brain says they are saying. There is not even a trace of guile in their brain pattern.
Or, let's say that an economist obsessed with "signalling" claims that it's everywhere -- that this person is signalling, and that person is signalling, and everybody is signalling about something. Is there really so much of it, or are people often not even thinking about it? Well, we could find out -- look through all those brain scans of people posting on social media for signs of signalling.
Or, consider somebody like Glenn Greenwald, who likes to attack liberals for being "hypocritical". Are they really so hypocritical so often? Are they aware that they are, if what they write seems that way? If their brain scans are made public, we can find out.
I can see at least three dangers here:
1. Unless it works 100% accurately, somebody might get ostracized when it isn't deserved.
2. Privacy fears -- brain scans reveal more than just the narrow intentions you want communicated.
3. Creeping monopoly: even if it starts out being voluntary, it could quickly spread and become like Facebook, where you have to plug in, in order to even function in civil society.
The first two, at least, can be solved through the use of a trusted 3rd party service, whose job it is to verify your intentions and then give you a seal of approval on social media. A check-mark beside your name. Even if they can't verify exactly what you hoped would be in your brain scan, they might still be able to say something good about your intentions. e.g. "Intentions are good; definitely not a hypocrite; but intentions are not exactly what they claim." (Of course, there's the question of what "good" means. That, too, can be taken into account in explaining the readout.)
If mass-scale use of such a service actually occurs (and something very much like it probably will, eventually; though it might become implicit in how we communicate via BCI), it could pop filter bubbles and make politicians more honest. It could also destroy the lives of a whole generation of "thought leaders" that are not who they claim be, proving them to be a lot more petty and cunning than their followers ever imagined. Would it be such a bad thing to expose them like that?