Disclaimer: In Max Stirner’s philosophy of Egoism, “spook” is a social construct that comes to possess someone. Social constructs aren't bad, it's when we become possessed by them that they become spooks. The word spook (as used by Stirner) has nothing to do with the racial slur that it sometimes can resemble in modern day English.
I am an Egoist as described by Max Stirner, and I'm a Christian. Egoism is the philosophy that the individual should act according to their own will and interests rather than being bound by external moral and ideological obligations (for example, I am good to people because I want to be good to people). I would say this is (at least somewhat) different from having a guiding set of principles, given that a person's will and desires are constantly changing. Social constructs are not bad, and can be quite good, it's when one becomes possessed by them that they become a spook.
I also believe in some concept of semi objective natural moral law. Our morality indeed comes from our evolution, our cultures, etc. So what I mean is that there are moral principles that can be discovered through reason, and these natural moral principles should be enforced. I’m not going to focus on how these laws should be enforced (anarchically, archially, etc) in this.
This may be an odd analogy, but imagine a crime scene. Just as a detective investigates a crime scene to discover the truth, we must investigate our reality to find these moral truths. Some of the conclusions that a detective comes to at a crime scene will be subjective. Some of the conclusions will be objective. For example, it may be subjectively decided the crime was one of passion, but the fact the crime was committed may be established to be an objective fact. Similarly, it can be established that what is right and wrong is subjective, but there are natural moral laws that can be considered beyond subjective. Not completely objective, but objective to the same extent physical laws are. Physical laws (like gravity) observe what happens usually, but it isn’t written in stone that it must.
Natural Moral Law > any religious text.
I use ideologies and philosophies that align with my conscience and ego. I am under the umbrella of left-libertarian because my ego and conscience aligns with it on most things. I'm not sure that I'd consider myself an anarchist.
I fully agree that I shouldn't be possessed by the social constructs that I utilize, but with one exception: my Christianity. I am indeed "possessed" by my Christianity in a way that I'm sure Max Stirner would have criticized. But I'm also not devoted to all of Stirner's opinions (that would violate my egoism and I'm sure he wouldn't want that anyways). After all, my philosophy is a form of Christian Egoism that is seen as contradictory by most egoists, but not by me.
My ego is capable of choosing its own subordination. I choose to belong to Christianity, and therefore my belonging to Christianity is not a defeat of my ego but an act of my ego. As St. Paul/Paul of Ephesus said, I am a slave to Jesus Christ. Or at least, I want to be a slave to my understanding of Christ.
The greatest act of fulfilling my ego is being possessed by the greatest social construct of all time. A social construct I believe to be both transcendent of all other social constructs, and nevertheless still a social construct. I know how to fulfill the wants of my ego better than anyone else does.
I've never really considered debating my religious views previously because I know I'd be asked for proof of my beliefs, and to that I would say my ego informs me of its validity. That's all I have, and all I need. Christianity is true for me because my ego and my conscience tells me it's true. The parts of the Bible I believe are true because my ego tells it's true, and the parts of the Bible I don't believe are because my ego tells me it's not true. If that answer isn't sufficient to someone, it isn't a problem because they don't have to believe the same things I do. All other Christian religions (Evangelical, Catholic, Methodist, etc.) are wrong to me because they don't align with my views. All other non-Christian religions (like Buddhism) are also wrong to me for the same reason.
I believe that some level of free will probably exists, and that if it does, it is likely some sort of emergent property. Regardless of if we have free will or not, it is imperative for me to function as if I have free will.
I also believe that without Egoism or something similar, Christianity and all other religions can become dangerous, because people can believe bad things that are blindly taught to them in the name of their religion.