There must be a reason why the characters attracted you to their cause in all their veering asshattish glory, and you (the general 'you') should write and show it as such. Like, I loved Sirius Black, and understood that it was his personality that made him strong enough to reject the tenants of his family and in the same breath, made him a proper asshat. So yeah, the best stories are always the one where you accept ALL aspects of the character and write them as is. But a LOT of people tend to write the character through tinted glasses and the stories suffer as a result.