The fact is, you're all talking about them. And that's all they're trying to achieve at the moment - they understandably want to keep the story high up the news agenda, regardless of what people think of them. And rightly so, IMO.
Dignified silences are very noble, but if they hadn't been appearing on Eurpean TV channels, meeting the pope, encouraging sporting events to feature the story, and "swanning around", far fewer people in Europe would be aware of their daughter's disappearance. And mobilising the European public is going to be far more helpful than them silently and frantically searching Portugal on their own.
Nobody's going to want to find Madeleine any less, just beause they dislike her parents.