Błędnie: His being opportune is the real explanation of his decision; he has never had any higher motives. Poprawnie: His being opportunistic is the real explanation of his decision; he has never had any higher motives.
Słowo ‘oportune’ znaczy „dogodny”, np. ‘Let’s wait for an opportune chance’ („Poczekajmy na dogodną okazję”).
Natomiast słowo ‘opportunistic’ znaczy „oportunistyczny”, np. ‘He is too opportunistic to protest’ („Jest zbyt oportunistyczny, by protestować”).