I've always approached the Sani Sabik as a religion. Some people approach it other ways, like a philosophy, but to me that seems to cheapen it. It would be like someone calling themselves a Christian but the only element of that is they treat others how they wished to be treated. In my course of creating Sanguina I read all the PF associated with the Blood Raiders/Sani Sabik (not much) and extrapolated from there. It's very, very vague, but the one thing that it says the sects have in common is the use of blood.
From here we have to extrapolate a few things from the PF. Firstly, we know that the Amarrians were some form of Catholic. Note this is stated by CCP, you could not tell that just by looking at the in game depiction of them, or the scriptures. One of the central tenants of that faith is that the blood of Jesus, having all sorts of properties that I will not get into here, redeems the sins of everyone. Now, fast forward about ten thousand years and a few rises and falls of civilization. Strip away most of the religion around it to the following beliefs. Firstly, we are all imperfect (this is self evident to anyone). And, most importantly, that there is a paradise, but the cost is blood. It's not too much of a stretch to see this.
Now, obviously this is a rather high price to pay, if you are the one paying it. The best solution is to find others and make them pay it for you. So you wind up with this Darwinian religion, wherein the strong take from the weak for their redemption. Since civilization was in the dark ages, it's easy to see where this mindset comes from.
Now, a few words about Sanguina. She's not evil. It's too easy to portray the Sani Sabik as blood crazed lunatics (coughs and looks a bit embarrassed). But we're not going there tonight. Mosab Hassan Yousef, the son of the founder of the terrorist group Hamas, renounced his father's actions and converted to Christianity and spied on Hamas for the Israelis. Sometime after moving to the US he gave a statement along the lines of (paraphrased), 'my father is not an evil man, he just fallows an evil god.' We're not getting into that debate tonight either. The point is that Sanguina is calm, loves her daughter, has fun and, oh yeah, kills children. She does the latter because she truly believes that it is the only way she can be saved and get to paradise. I would reason that many of the Sani Sabik also feel the same way. Not that there are not blood crazed lunatics in the Sani Sabik, but most are probably as balanced as any other person in New Eden.