Weapons for Weyland

From the first Alien movies it is clear that that the "company" (Weyland-Yutani) wanted a Xenomorph or Facehugger for its "weapons division". But why? From what I can see, Weyland seems to want to better the planet and the lives of people (and probably control them a bit as well), what with all these inventions and people living longer through the application of technology. Is this all powerful company afraid of something or considering going to fight a war or defend themselves? It is possible that toward the end of Prometheus it is revealed that the engineers and/or jockeys have every intention of recolonising/reclaiming Earth as their own (now they know it has reached a certain level of development) even if one of their ships is downed. And Weyland creating a weapon based on Xenomorph biology may give humans a chance of fending off any attack, seeing as it is possible the Xenomorphs may have caused the partial demise of the Space Jockeys. It may be the one thing the aliens are afraid of and Weyland just wants to defend the planet, but obviously keeping the alien threat a secret. Perhaps this could be one of the alleged open questions left at the end of Prometheus, and Weyland's secretive intentions are actually for the good of the human race.