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: 
Suspicion is suspicion. Whether your suspicion is based on assumptions or not, it is always the feeling or belief that something may be possible or true.

You can't have a bad suspicion nor a good suspicion. What you suspect to be possible is really what is at stake here, whether good or bad. The suspicion itself, however, cannot inherently be bad or good, only the actual event.
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."