I wonder what's the Death Eaters' opinion of phoenixes. If they agree that they're a force for good, seeing one of them in Dumbledore's retinue should make them ask themselves a few questions (a generic problem whenever you put a public, physical moral compass in any world, really - it becomes much harder for the villains to delude themselves into thinking they're heroes). Perhaps they think they're just creepy, winged endorphine peddlers.
Phoenixes encourage you to go out, and throw yourself full-strength against a problem, regardless of whether you can solve the problem, regardless of your chance of death.
To a slytherin, this is simply irrational. Gryffindor is brave, AKA foolhardy. Slytherin is devious AKA rational. The gryffindor method is the phoenix method: ignore the dangers that stand in the way of your goal.
Update: Discussion has moved on to a new thread.
After 61 chapters of Harry Potter and the Methods of Rationality and 5 discussion threads with over 500 comments each, HPMOR discussion has graduated from the main page and moved into the Less Wrong discussion section (which seems like a more appropriate location). You can post all of your insights, speculation, and, well, discussion about Eliezer Yudkowsky's Harry Potter fanfic here.
Previous threads are available under the harry_potter tag on the main page (or: one, two, three, four, five); this and future threads will be found under the discussion section tag (since there is a separate tag system for the discussion section). See also the author page for (almost) all things HPMOR, and AdeleneDawner's Author's Notes archive for one thing that the author page is missing.
As a reminder, it's useful to indicate at the start of your comment which chapter you are commenting on. Time passes but your comment stays the same.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: