Bullshit is what comes out of the mouth of someone who values persuasion over truth. Truth is about communicating information. Vague language communicates less information than precise language.
It is important to distinguish vague language from general, poetic and simple language.
- Vague language is distinct from general language. Vague language communicates less information than regular language. General language communicates more information than regular language. Broader claims are more easily falsifiable than narrow claims. The more falsifiable a claim is the stronger a claim it is. The stronger a claim is the more information it communicates.
- Vague language is distinct from poetic language. Poetic language has very high information density. High information density is the opposite of vagueness.
- Vague language is distinct from simple language. Simple language is easy to understand. Simple language should be used most of the time because simple language is more convenient than complicated language. In disagreements, simple vague language should be replaced with precise language—even at the cost of some complexity.
Deliberately vague language increases vagueness without increasing generality, poetry or simplicity. It obscures the truth.
- "No evidence" is vaguer than "evidence of absence".
- How many shares of a company you own is vaguer than what percentage you own.
The people with a need to obscure the truth are those with a political or social agenda. Vague language is endemic to taboo subjects. Deliberately vague language is such a reliable signal of taboo subjects that you can use it to discover hidden taboos. If you find yourself or others using deliberately vague language around a topic it means there is something you can't say.
The most precise language is numerical. If numbers could be used but aren't then you are dealing with a taboo subject.
- "Smart" is vaguer than IQ thresholds.
- "Fit" is vaguer than BMI and bodyfat percentage.
You can even use vague language to figure out which subjects are bullshit and which people are bullshitters.
- Modern art uses vague language. Drawing manuals like Scott McCloud's Understanding Comics: The Invisible Art use precise language.
- Literary theory is notorious for using vague language. Brandon Sanderson's lectures on creative writing use precise language
Almost all humans, in almost all contexts, value persuasion over truth and have a social agenda. Condemning all human behavior that is not truth-seeking is condemning almost all human behavior. This is a strong (normative? prescriptive? judgmental?) claim that should be motivated, but you seem to take it for given.
Persuasion is a natural and desirable behavior in a social, cooperative species that is also competitive on the individual level. The main alternative to persuasion is force, and in most cases I'm glad people use persuasion rather than force. Truth-seeking would also fare worse in a more violent world, because truth has some persuasion value but little violence-value.
Truth is instrumentally useful to persuasion inasfar as people are able to identify truth and inclined to prefer it. I'm all for increasing these two characteristics and otherwise "raising the sanity waterline". But that is very far from a blanket condemnation of "valuing persuasion over truth".