August 12, 2013 10:29 PM EDT
While do agree that they are neutral, in the end I think it really all boils down to who the current Listener of the Dark Brotherhood is or if they even have a listener. In the Skyrim when you encounter the DB they are sans listener, and that coupled with Astrid's rather cynical view of things makes them come off as more evil in contrast to the DB in Oblivion who had a listener, speakers, & the Black Hand to maintain the hierarchy & traditions of the organization.
Kyrielle also has a good point tho, entry/recruitment into the DB is far less strenuous than the Morag Tong, allowing for a more... colorful array of members in the DB, thus distorting their neutral status.