Why does the word "incident" have a negative connotation associated with it?
Solution 1:
M-W cites the negative connotation of incident as third:
3 : an action likely to lead to grave consequences especially in diplomatic matters.
- a serious border incident
The above connotation is an euphemistic usage from the beginning of the 20th century:
Euphemistic meaning "event that might trigger a crisis or political unrest" first attested 1913. (Etymonline)