[quote=@Nate1008]
<Snipped quote by Sierra>

The Infestation may create temporary alliances for a while, but back-stab them later. Also, the Infestation may trade food for other resources anonymously, and may ally with other infestations like The Lucifern hosts.
[/quote]

Just saying, having a history of backstabbing isn't going to make you a lot of friends. The entire fact that most people find infected beings to be repulsive/horrid/disgusting/etc already makes trying to interact with them hard enough. The two combined means that nobody is going to trust you enough to backstab. 

Having the end goal of eating everything in the galaxy is also a really hard sell to just about everyone. The Lucifern Hosts are going to see the Infestation as more of a threat than anything just like everyone else since they, just like everyone else, don't trust the people who want to eat everything including themselves.