My concern with all-or-nothing validation of the sort you're suggesting is that sometimes the invalid data is data that isn't your concern and doesn't matter to the task you're trying to accomplish. It doesn't even have to be a mistake on the sender's side; maybe something evolved, maybe you made the mistake. I prefer defining the minimum I need for a specific function, instead of defining exactly what I expect. For much the same reasons as we scribble in the margins sometimes.