Arbiter

No.. he didn't.


Also, the Forerunner did not create the flood, the server 4 video proves this.

I really don't think the monitors are as smart as we believe they are. Think about it. If the forerunner in their strife with the flood have figured out that they had some sort of sway over AI's/Monitors (as seen by GM and 2401 PT) Then wouldn't it make sense that they programmed the monitors to believe that they have all perished during the first activation of the halos. 343GS only says the word "forerunner" ONCE. every other time he refers to them as "my creators". Now if his protocol states that halos activate = all flood food dies then he would assume that its true. GS cannot physically confirm that every forerunner that existed has perished.

So isn't this question essentially answered with the unlocking of server 5?

Towards the end of their long battle with the Flood, the Forerunner discovered another, newly developed, lifeform – humanity.

"The inhabitants; these unique denizens, must be researched.
They may hold answers to our own mysteries."

"{/What irony that we discovered this treasure, only at the end of things./}
{/But what fortune that we still had time to save them./}"

And decided to make them the recipients of their legacy, after they and all other sentient life had been wiped out. Humanity would be saved by the Ark: "The thing we built on that world will vouchsafe their lives", and when they were ready, it would provide them with the answers: "I promise you the answers lie in the Ark", allowing them to reclaim the Forerunners knowledge and become Reclaimers.

"If the plan fails,
{/And the adversary succeeeds./}
it will remain an enigma forever
{/With no-one left to reclaim it./}"

From GoO:

She bent closer to the last pod and ran her fingers over the forerunner icons along its side, translating as she did so: " 'That which must be protected…behind the sharpened edge of the shield…beyond the reach of the swords…for the reclaimed.' No, that’s not quite the correct meaning."
"Reclaimed…" Ash echoed. “Maybe 'Reclaimer'?"
"Yes. A title. Specifically, an honorific. (p. 337 - 338).

Unfortunately, it seems humanity never discovered the Ark, so they never found out the truth (and whatever treasures the Forerunner saved for them), something GS must have been unaware of, which is why he was confused by MC's apparent ignorance about the purpose of the Halos.

I suppose the real question now is, what is the Ark's intended purpose?

{/But perhaps one day it will be used for its intended purpose./}

Either way, it sounded like the Forerunners had no choice, at the time, but to accept the annihilation of themselves in order to ensure the security that whatever knowledge they had about anything and everything wouldn't be consumed/absorbed by the Gravemind. It is about the same as the UNSC issuing the : a countermeasure that ensures the safety of Earth and all human colonies from being located and destroyed by the Covenant. Also, by isolating us from the Flood, it's possible (with the Ark) they want humans to continue (the fight against the Flood) where the Forerunners had left off.