> Most of those people are doing it intentionally though

Sometimes, yes, but also because people misunderstand are make invalid inferences.

> I disagree. A big part of intelligence is realising/admitting you don't know. That you are missing information. And you don't just fill it up with BS. You going find that information.

Notice how you inferred missing information here. Ironically you inferred the wrong intent behind what I said. I did not suggest "filling it up with BS" was useful nor desirable. It is a possible interpretation of what I wrote, I will accept, but it requires assumptions - one does not follow logically from the other.

What I actually suggested is that a willingness to fill in details is necessary, not that filling it in no matter what or without having something reasonable to fill in is necessary.

I agree that a big part of intelligence is realizing and admitting you don't know. I does not conflict with what I said. With the caveat that you can not always admit to not knowing every little detail you don't know - if you did you'd be unable to function.

My point was that we rarely "know" anything with 100% certainty, and so the question is not if we assume, but at what perceived level of certainty we set the bar. If I write "2+2=4", it is not a great sign of intelligence to ask me if I am using standard arithmetic or use special rules, unless you have context to suggest I might be or I have reason to interpret it as you being a smart-ass about it.

It is a core sign of intelligence to understand from context which bits of information it is likely justified to fill in when missing based on the fact that it makes a statement, or a behaviour, consistent if interpreted using that information.

So to restate, the willingness to fill in details is essential to functional intelligence, because without it we'd be forever unable to draw conclusions without continuing to seek clarifications of additional unstated assumptions.

Just reading this involves making assumptions about the degree to which my use of every individual words conforms to standard English usage, and indeed starts with the assumption that this is English to start with. Granted it is an assumption with exceedingly high certainty, but I have not told you I am, so it remains an inference whose certainty will get ever closer to 100% as the length of the conversation makes alternatives more and more unlikely.

When the uncertainty increases, sure, the intelligent choice at some level becomes to admitting that you don't know. Learning how to recognize the threshold is also essential to functional intelligence. Assuming much and too little both leads to conversations that go nowhere.

> Do we?

Yes, we do. We tell kids to not make things up in contexts where we expect them to answer us based on reality all the time. I'd be willing to claim that not an adult alive has not been told to stick to the truth a multitude of times. How effective that admonishment is certainly varies, and yes we sometimes also teach kids there are contexts where lies are better (whether we teach them that intentionally or not). Older children will certainly be better suited, including in terms of brain development that does not per se require reinforcement, to tell facts and fiction apart, but young children tend to hold a whole range of beliefs that appear genuine that has no relation to reality, and for many people some such beliefs persist for a long time when uncorrected.