It doesn't mean the opposite, it means quite what it says. 'All but' means 'almost' or 'nearly'. The confusion comes from the elision inherent in the phrase. "They were all but exterminated by the Jedi" could also be written "They were hunted, tortured, maimed, and killed--all but exterminated by the Jedi". In this example, the reason 'all but' does not include verbs like 'tickled' is due to the principle employed in all communications, 'noscitur a sociis' (latin, 'it is known from its associates'), which requires phrases remain topical.