I'm not sure whether I agree as to the extent of Harry and co's passivity... When it comes to the war with Voldemort, sure they all sat around with thumbs placed firmly up their puckered assholes, but before the real conflict started, Harry regularly went looking for trouble and found it. Not many eleven year olds would take it upon themselves to try and stop a plot involving several older, more dangerous wizards and yet he showed his 'Gryffindor Courage' by getting involved in the whole Quirrel mess with his friends. They have actually been proactive during certain aspects of the books... When Draco or other Slytherins are doing something suspicious they always get right to trying to get in his business and they did indeed manage to save the school on several occasions.

The point I'm trying to make (and getting away from) is that during the first 3 books the trio takes a lot of proactive action. Sure they are just reacting to events already going on in the school but they still took the burden of action on themselves, Harry serving as the reluctant hero the whole way. True passivity would have resulted in a ressurected Quirrelmort (assuming Dumbledore didn't do the supremely irresponsible thing by willingly allowing a possessed teacher into the school just to give Harry a preview of the life he would live), a dead Ginny (wouldn't have been so bad), and Sirius Black the soulless vegetable. True passivity would have been the trio finding out about the basilisk and saying, "ah well, let's go to lunch."

Where the passivity really becomes annoying is post book 4. I assume that Rowling had difficulty balancing the genre and the subject matter because her portrayal of the conflict between Voldie and the Wizarding World is pretty shitty. The ministry falls at the drop of a hat, the Order of the Pheonix proves basically ineffective especially at taking any sort of preventative measures for warfare and Harry, Ron and Hermione are removed enough from the action (stuck in Hogwarts) that having them making any real preparations would have been unrealistic.

So is Harry a passive hero? To an extent. He did roll over to die once learning of his scar's significance, but he always reacts to any perceived injustice. Harry is not passive, I would say reactive is basically the perfect word for it. But passive and reactive are not mutually exclusive in the same way proactive and reactive are and so I would have to say that he is not passive.

That was a lot of typing for a little bit of point