Wait... you're not seriously suggesting that Destroy isn't supposed to be a conclusive victory too, are you? Control I can see, even if that's mostly you projecting, but what's inconclusive about Destroy?
In fairness, the red flavor is perhaps the most inconclusive of the three. Does Shepard live? Do the Geth really die? Are all the Reapers gone, or might some have survived if they were far enough from a relay? Did anyone survive on the Citadel? Is Earth toast?
Some of those were sort-of answered in the EC, but in the original there is a whole lot of guesswork involved. As I understand it, that was intentional--Mac wanted to leave people with the general sense that the civilization of the galaxy had been destroyed, figuratively nuked back to the stone age, leaving people to wonder how long it would take for a galaxy-spanning civilization to re-emerge and what it might look like.
With blue, you know at least who's in charge of the clean-up. If you can accept green, you're probably willing to take what you see in the game at face value and not really worry much about the rest. Red's the one that leaves you wondering.