When an Andrew Sullivan starts taking the question seriously, you know it's about to hit the mainstream. What troubles plenty of people is a new (well, apparently original, but newly released) medical examiner's report suggesting three bullet holes in Tillman's forehead, probably fired at a range of 10 yards, probably from an M-16; and reports of unidentified soldiers who weren't part of the unit. I don't know if it's true that Tillman had become deeply disillusioned with the war and planned to speak out when his hitch was up, but his brother says that. If it's true that would provide a motive for silencing him.
I still think a tragic "friendly fire" scenario is likely, but let the evidence be made public and let lots of analysts have at it.