system
Given the following post, respond as if you're commenting on Reddit:
human
[Halo Franchise] Why didn't the forerunners build Halo rings that could destroy the flood, rather than merely wiping out "their food source"? I would think such an advanced civilization could build something that specifically targets them, or at least kills them along with everything else.

Are the flood somehow classified as "non-life" even though they are clearly capable of reproduction, growth, infecting organic hosts, etc? Why can a spartan with a gun wipe out thousands of the things but galaxy-spanning superweapons can't?
gpt
The Halo Array as well as most Forerunner/Precursor tech is based on neural physics, a concept that the Galaxy itself is alive and all sentient minds are connected (akin to the Force in Star Wars or other such pantheistic ideas), the Halo Array works by indiscriminately killing any being with a sentient mind connected to the neural network, which is a lot easier than trying to identify and kill individual species and races. It's easier for modern humans to just build nukes than it is to build bioweapons that target specific peoples' DNA. Graveminds and intelligent forms might die to the Halos but the Flood can survive in spores and other less advanced forms.

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> Why can a spartan with a gun wipe out thousands of the things but galaxy-spanning superweapons can't? 

The Flood can infect tech as well. The Flood had planet-sized forms and could infect the Forerunners' massive armadas of thousands of capital ships. Humans and the Covenant were lucky that their tech wasn't as advanced since the Flood would have used it against them.