This is a pseudo-fictional scenario, we suppose telepaths exist and that governments keep them secret.
Why?

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Fun question

It would be simple. Telepaths would just be another surveillance and encrypted communications technology. Maybe not as reliable as our current technology (accuracy aside, if telepaths exist at all, there's other telepaths out there that AREN'T controlled by the government in question, or ARE controlled by foriegn governments, and there's absolutely no way to tell who could be "listening in"), but the benefit would be that no matter how advanced anyone's counterintelligence measures got, the government employing psychics would always have a "brute force" surveillance and, if not encrypted, at least obfuscated communications method.

Also, telepaths could simply read encrypted messages off pieces of paper or computer screens to other telepaths, which would allow for short encrypted communications as well.

Of course, like all our other toys, most governments would eventually let the world know about telepaths - once they got something better, of course.

The downside, is that it's extremely hard to sell human beings as war munitions to many countries, especially countries that take issue with slavery. Not all, but most.

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