It's not. Most of Pink Floyd's Animals album is trash, except for Sheep which I think we can all agree on being a fucking great song from a great band.
Steven King's The Dark Tower series is trash, except for The Gunslinger (and, okay, the final chapter of the final book The Dark Tower), which I think we can all agree on being a fucking great book from a great author.
The Lamiids's Solanum species of plants is poisonous trash, except for Tomatoes which I think we can all agree on being a fucking great fruit from a fucking great subclade.