Nothing is allowed to stand in the way of their "mission" and they are determined to "convert" all who they come in contact with. Sound familiar? Seeing as Gene Roddenberry was an atheist, I have to think that the creation of the Borg was intentionally based on religious fundamentalists. Once a being becomes a Borg, it is very difficult to break away, just as it is difficult for members of fundamentalist Christianity (or even moderate Christianity for that matter) to leave the "flock."
Here is an excerpt I found at Borg Xenobiology Database:
The immense knowledge of all the assimilated Borg minds function as one, and each Borg is part of a giant subspace communications network called the Borg Collective. All critical information is relayed to each Borg through this network, allowing the instantaneous adaptation and reaction to any outside factors. The hive society of the Borg is extremely specialized: the decisions are not made by the Borg themselves, rather, the needs of the Collective determines their actions.
To the Borg, individual thought and action are considered imperfect and weak. They travel through the universe in their cubicles or spheres seeking new civilizations to assimilate into their own consciousness, or in their words, "add the biological and technological distinctiveness of to our own". They don't simply assimilate individuals, they strip cultures, races, entire worlds of their identity. New species encountered are classified with numbers and referred to as such, further eliminating the distinctiveness of the species. The emptied shells of assimilated individuals are integrated into the hive while their understanding and technology are added into the Collective. If a Borg drone dies or is beyond repair, his memory will still be retained by the Collective. So in a sense all Borg are immortal.
Negotiation is irrelevant. You will be assimilated. ~Collective 67kb
Freedom is irrelevant. Self-determination is irrelevant. You must comply. ~Collective 117kb
We are the Borg. Resistance as you know it is over. We will add your biological and technological distinctiveness to our own. ~Collective 162kb
You will become one with the Borg. You will all become one with the borg. ~Locutus 120kb