The relevant paragraph from the article I linked to:
Now when Thief hits Copper, you’re glad and they aren’t and that’s that. When Pirate Ship hits Copper though, everyone’s happy. You don’t want the Copper and they want the token. You don’t want them to get the token. In a two player game, trashing your Coppers first can help here. With more players, you probably can’t get everyone to slow down the Pirate Ship enough. Instead, just coast to victory by building your own efficient Copper-free deck, courtesy of them stealing those Coppers for you. Pirate Ship can cause some groups problems, I think because it’s an answer to itself – Pirate Ship makes you want an action that makes money, and hey Pirate Ship is one of those. So everyone plays Pirate Ships and Pirate Ship seems unbeatable. It is so beatable though. Trashing your Coppers is normally something you give up several turns to do; having it done for you leaves you in fine shape. And you don’t even have to do without money – eventually the Pirate Ships will stop attacking. You can even feed Pirate Ships by gaining Silver – say, with Explorer – and it can all work out.