- last post: 01.01.0001 12:00 AM PDT
Read this:
http://www.bungie.net/Forums/posts.aspx?postID=5560063
It'll explain why the halo's were created to kill everything.
In short - The flood parasite can not be exterminated on a wide scale level, because they are a microscopic virus there is no way to kill absolutley every instance of them. So instead hte Forerunners built a the halos to kill all sentient life with suffienct biomass to be a host for a flood form. The infection forms bury themselves into the host's chest and their tenticles spread throughout the host and take control of their body via the nervous system of hte creature. [theory] To stop this process, the Halo's send out a specific radiation that basically scrambles the nervous system and makes it impossible for the flood to intergrate and take over the host. Unfortunantly it also kills the creature.
Read the above theory, it makes a helluva lot of sense and accounts for a lot.