In the 2000s, when used in a
lawyer-created public apology, a word that demonstrates that the
person concerned (eg. a sportsperson) knew their actions would be wrong before they acted, do not regret their actions for one second since, and are annoyed they got caught out and are forced to make a public apology to keep their career going.
When used by another authority such as their
coach, using 'unacceptable' implies the latter is also annoyed that the former got caught out, is forced to make a public apology and that the
mud sticks to the authority by association.