Speaking of dark energy

The Dark Energy plot had even more issues than the one we got. For example, the Reapers having Dark Energy utilized in the tech they left behind so the races would develop along using Dark Energy sure seems to be counterproductive if their goal is to limit or stop it.

It wouldn't be biotics, it'd be eezo itself. Basically, when present in the right configuration/amount in a solar system, it could cause a Haestrom-like effect, which kind of does make sense superficially (again, it's Mass Effect, so don't get down to numbers). In general, something like a star creates massive EM fields and emits charged particles. Eezo needs electrical current to generate dark energy/mass altering effects, which could be provided by electromagnetic induction. Project that ME field back onto the star itself (say, if the eezo is geometrically arranged in the right spots or enough is there, since eezo physics are fictional, you have quite a bit of latitude there) and the star would go super nova more quickly (again, like Haestrom). Supernovae in turn generate eezo, so it's an exponentially deteriorating situation, just on a massive time scale and spatial scale (which is something that you kinda need for the reapers, it has to be something that would be tough to grasp for a species that doesn't live for over a billion years or so).

Now, With increasingly eezo dependent civilizations that shuttle the material around the galaxy, any interstellar civilization would participate in making the problem worse.

The reaper cycle is then intended to cut the growth of these civilizations back in order to preserve the galaxy's state as long as possible while they are trying to come up with a better long term solution.

I think just logically in the broad strokes it could have made sense. Of course, you'd need to color out the details but that's why I'm saying, if introduced and developed gradually over the cause of ME2 and ME3, it could have made for a great plotline.

The Reapers also permit races to find relics of the previous cycle, and to develop to a high enough technological level to rediscover the mass effect. They don't have to do either of these things.

The bare bones of the plot are interesting. Probably would have gone through several rewrites beyond the initial idea we'd heard about. It does seem, as some have suggested, that it was worked into MEA in the form of the Scourge.

For once, I am with alanc9. I think I would have hated it too if the reaper's motivations were kept secret and mysterious. To me, scifi stories (and this kind of space opera scifi especially) are all about exploration, about discovery and about figuring shit out. It would have been really disappointing to me if we defeat the reapers somehow without figuring them out in some capacity. To me, since ME1 the key to defeating them always had to come from understanding them better.

So if harbinger just said they did it because they could that would be fine? Or maybe that they did it  to make sure that the organics never got far enough to be a threat?

They essentially said that they did it so that organics never got to be a threat, so I'm really not sure what you're getting at here since I'm the one person here who is probably the most OK with ME3's endings as they are.

Why would the Reapers have to have to do anything with Dark Energy? Could just be an interesting side story. Not every interesting thing needs to be connected to the reapers