You shared a very powerful story. I think you're right that it's important that anarchists remember that things like that can happen.
However, it's also important to recognize that what you described happened under governance. It was not the result of a lack of laws and enforcement; it happened despite their existence.
I could expound upon the governmental policies that contributed to this incident, but you freely admit those, and, more importantly, it's beside the point. People will do bad things, with or without governance. So, what factors cause people to behave in this manner and what measures might prevent someone who is inclined towards doing this from doing it?
Government promises answers to these questions, and action based upon them, but it comes with a price. The price is that they will demand special powers and allowances where everyone else is restricted. The price is that they will provide no defense when it is the government itself committing those acts, which, through the necessity of supporting itself, it will.
Anarchy doesn't spring from an inherent trust in human nature, but rather from distrust. If you don't trust people to be good to each other, then why would you trust some of those people with power that can easily be abused? Utopia is the idea that someone else will look after you and take care of all of your needs. Anarchy is an understanding of reality: You need to take care of yourself.
No, this does not preclude working with others or any other strawman nonsense. It is assertion that each individual must, with or without government, be aware of their surroundings, seek out information, and take measures to protect themselves. Anything less is baseless trust and blind faith, no matter what socio-economic structure is utilized.