Well yes. It's definitely a good question to ask. But before you even put yourself into a questioning or doubting frame of mind, how do you get there? What are initial clues that something is amiss? If you are a frequent consumer of a certain news or commentary program that had elements of propaganda in it, how would you know it was actually a brainwashing tool?

@Flowerwall Perhaps sadly, I am always in a questioning frame of mind, fortunately I am a natural sceptic, I trust nothing and nobody anyway. Therefore I always assume that everyone lies by default, and that everything I am told is untrue, then I put it to the, 'who gains' test, and if I can find no actual reason why someone gains, then I assume a possiblity that it may be true. But my default possition is to assume everthing is untrue.

@Fernapple I don't think most people operate under this idea "I trust nothing and nobody", I don't think most people should. By and large most systems around us are good systems meant to encourage our well being. It is not a good approach to constantly mistrust everything unless you can accurately put it in context (probably in your case you are older and have had more life experiences and so it DOES work for you) But the beginning clues I see are viewpoints that are one-sided and cannot withstand any questioning or counterarguement. In my mind it's a sign of absence of balance, a dismissal of reality.

@Flowerwall One sided is certainly a good clue. Another is lack of nuance, and qualification, it is human nature to be lazy, a good thing once, active brains use a lot of food, and when apes like us had to earn our food on the plains of Africa, at great risk and effort, conserving it was useful. But today looking for easy simple answers is a sad legasy of our evolution, very close to being one sided , lack of detail and nuance therefore is one. Certainty another, for much them same reason, people who think honestly and value truth always doubt, while confidence again denotes lack of care and effort, plus perhaps, a strong wish fullfilment drive, which shows motives other than the pure wish for truth, such as the wish to impress, or to avoid fear of the unknown. (Good word, 'perhaps' rarely used by the untruthful, qualifiers are generally good signs.)

But do not undervalue the distrust everything possition. Because being mistaken, even honestly mistaken, is our default state. It is like the old argument about religion. There are at least ten thousand gods, and a hundred thousand sects worshipping those gods, most (Most another good word.) of which claim to be the only true religion. And as the saying goes, they can all therefore be wrong, but only one of them, at most, can be right. Human culture was for the most part built by people who started with errors but then rather than throw the old errors out when problems arose, chose to add more untruths to plaster over the cracks. Because the alternative of throwing out the old errors and starting again, takes courage and effort. So that in the end human culture becomes a vast pile of untruths, with just the odd truth in there by accident, and all the lies piled on top of one another in mutual support. Try researching "adding epicycles" if you have time. Human culture is simply not a good guide if you are looking for truth.

Also if you have time Richard Dawkins on religions as viral infections of the mind, is well worth looking into, though I think that he is mistaken in limiting the theory to religions alone, and not seeing all of culture as a series of viral infections.