Question: What is a single word to convey the sense of "inaccurate suspicion," but that tends to infer a bit of unfairness, such as 

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> It is immoral to use brutal force in response to [inaccurate suspicion].
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Answer: 
The precisest word in English to this concept is "surmise".

* The OED defines: "To form a notion that the thing in question may be so, on slight grounds or without proof; to infer conjecturally."
* A surmise is (obsoletely) "An allegation, charge, imputation; esp. a false, unfounded, or unproved charge or allegation."
* A surmiser is "One who makes a surmise or conjecture (esp. ill-founded); [...] one who suspects evil of another."
**bogey** noun (FEAR)

[ C usually singular ] (also bogie); (bogy)
something that causes fear among a lot of people, often without reason:
the bogey of unemployment

<https://dictionary.cambridge.org/dictionary/english/bogey>

"a mere bogey" gets the idea over even better but you wanted a single word.