To study them and possibly create or cure or a way to easier defeat them in case they ever returned. This was clearly stated in Cryptum/Primordium. The Flood are of extra-galactic origin and the Forerunners knew they would eventually return to our galaxy once again. It was actually worse not having any to study.

[quote][b]Posted by:[/b] ninjakenzen [/quote]Uproarious!

[quote][b]Posted by:[/b] ninjakenzen The Forerunners and Microsoft had a contract which would allow [i]Xbox[/i] to garner major success when faced with the fierce enemy of the period. The [i]Playstation 2.[/i] It was a stroke of genius, by containment, it would allow for the dynamic plot twist in Halo:CE and further sequels to be built around the external threat. Microsoft seized the opportunity and brought sequels upon sequels. The number of containment is vague to allow for new material. Thus the contract was healthy for Microsoft. The Forerunners in return were given recognition from the novels later on, as the race responsible for the inevitable events of Halo:CE [Wars] and so on. They would be remembered!. Both sides benefited greatly. Now they even have their own trilogy! Which is the sole reason they did it. Anyone else with a different response is just plain out lying. [/quote] Lol, thread saved.

Destroying all the Flood in our galaxy is a temporary victory/solution. We know that the Flood came from outside our galaxy, so killing all the immediate Flood threats is not a final solution, just a setback. The Librarian knew this and therefore knew that that the Flood threat could resurface. To ensure a true victory Flood samples needed to be kept and studied to come up with a cure, one which would properly and ultimately defeat the Flood. Hence why she proposed to keep samples.

[quote][b]Posted by:[/b] ninjakenzen The Forerunners and Microsoft had a contract which would allow [i]Xbox[/i] to garner major success when faced with the fierce enemy of the period. The [i]Playstation 2.[/i] It was a stroke of genius, by containment, it would allow for the dynamic plot twist in Halo:CE and further sequels to be built around the external threat. Microsoft seized the opportunity and brought sequels upon sequels. The number of containment is vague to allow for new material. Thus the contract was healthy for Microsoft. The Forerunners in return were given recognition from the novels later on, as the race responsible for the inevitable events of Halo:CE [Wars] and so on. They would be remembered!. Both sides benefited greatly. Now they even have their own trilogy! Which is the sole reason they did it. Anyone else with a different response is just plain out lying. [/quote] I actually laughed for about ten minutes after reading this.

Just a theory, but I'm fairly certain it is because the forerunners had no -blam!- clue what the flood was, where it came from, why it was unable to coexist peacefully, and if the flood they were fighting was the only flood in existance. so by keeping flood specimens for study after the halo array was fired, if another flood outbreak occured, they would perhaps have a way by then to defeat them without nuking all sentient life.

Because plot stupidity.

The Forerunners and Microsoft had a contract which would allow [i]Xbox[/i] to garner major success when faced with the fierce enemy of the period. The [i]Playstation 2.[/i] It was a stroke of genius, by containment, it would allow for the dynamic plot twist in Halo:CE and further sequels to be built around the external threat. Microsoft seized the opportunity and brought sequels upon sequels. The number of containment is vague to allow for new material. Thus the contract was healthy for Microsoft. The Forerunners in return were given recognition from the novels later on, as the race responsible for the inevitable events of Halo:CE [Wars] and so on. They would be remembered!. Both sides benefited greatly. Now they even have their own trilogy! Which is the sole reason they did it. Anyone else with a different response is just plain out lying.

To study them.