They’re intellectually lazy, socially weak, and likely traumatized from a childhood of fear. Religion provides simple ‘answers’ to complex questions; an instant network of fellow followers; and an ‘all powerful’ (if pretend) entity described by a charismatic conman more than willing to do their thinking for them…

Usually, people are raised in a belief system, taught it by their parents, and had it reinforced by their peers.

Thankfully, once children leave home for college they are usually exposed to humanism and secular beliefs, so often dump their childhood training.

The basic answer is because people think they need guidance. They want to belong and do right. Imaginary beings do not help with this however.

I developed a belief system because I was raised Catholic. I have a different t one now that I am non religious. Life is so much better for me now, and I haven’t murdered anyone or any of those other things that are forbidden. Lol. My main rule is “don’t hurt anyone”, be truthful and help others.....oh and to be happy. That’s pretty much it.

I also think that many adults eventually realize how little sense many of their beliefs make. But again they don’t have the strength or courage to face the identity crisis that questioning those beliefs entails, they fear losing their community, their loved ones. Many fear death and unknown, so they often react by holding on to those unconvincing beliefs even harder. Fear of death, fear of the unknown, fear of abandonment, fear of identity crisis are very powerful. We can’t all be brave enough to find a new identity or to live with unanswered enormous questions.

“You exist but once you die you will simply cease to be”, “You don’t go anywhere after death, you just stop being”, “Your life has no real value or meaning outside of your human experience”, “The universe doesn’t care weather you live or die”, “Nobody will know you ever lived or you ever existed in 20 million years”... and so on and so forth.

Don’t underestimate fear. Politicians win elections again and again by just using fear as they main tool.

Don't think the answer is a boolean of a simple dichotomy.

The answer most likely depends on a combination of various factors including both genetic and environmental. If a person (such as myself) who values truth (based on testable facts) over faith (belief without evidence), I have a "belief system" based on facts and finds faith based assertions void of merit. I maintain healthy skepticism and am weary of charismatic leaders. In my case nothing bad happened like a flood or meteor strike that cannot be explained. "I do not know" is a perfectly acceptable answer I will accept and offer when confronted with insufficient evidence.

If you restrict you definition of "belief system" to that of theists, I think many are just to damn lazy/afraid or mentally encumbered to examine the actual truth value " of the "Truth claims" they were indoctrinated with. On Youtube, "Trusting Doubt" and "Anticitizenx" have produced some really good examples of the psychology of belief. Worth your time to check out.

It’s not the leaders in my humble opinion. I’ve dealt with many religious “leaders” and they never impress me. They are usually bad examples of moral standards. They are self absorbed and don’t live what they preach.

An important key is IDENTITY and early indoctrination. That’s why churches put so much emphasis on teaching kids while they are young. Young brains are so malleable and easy to indoctrinate. A young brain is very very receptive. It’s designed to be so by evolution. That’s why it’s easy to learn languages, culture, math, sports, instruments when young. It’s much easier to brainwash a kid than an adult. That’s why many atheists consider early indoctrination child abuse.

Once the brainwashing is accomplished, as adults, religion becomes part of their identity just like culture, food, nationality and so on. We are tribal primates, like most primates. One’s religion becomes part of that person’s identity and anyone different is from “another tribe”. That’s why it’s easy to make people act as monsters in the name of religions, political views, nationalities. That is why religion is such a powerful way to control masses and it’s been used as such for millennia. It’s hard to convince a person someone from their own species is an enemy worth killing, especially if they look like them, act like them, feel like them. Race was a good way, but the problem is that a political or economical adversary doesn’t always have a different skin tone. So how do you get around that? You use other means such as religion or nationality or culture. But religion is so tied to rituals, community, practices that it’s a very powerful tool for tribal identification. “Disciples! Those barbarians don’t eat like we do, don’t pray the same God, don’t fast on these days, don’t respect our symbols, don’t read our books, don’t have sex the same way, don’t wear the same clothes!! Kill them all as otherwise who you are, and who your kids are will be destroyed!!”. So effective.

All you have to do it teach them young and everyone else can potentially become an enemy. That is why it’s so important not to teach children religion. Allow them to form their own identity with the least amount of influence. They can then pick a religion if they find it convincing as adults. Some do. But usually it’s not the norm and even when it happens, the religion they pick will not usually become part of their identity, they will not be easily convinced to perform evil actions in the name of the religion. If leaders attempt to manipulate them into acting in ways that conflict with their values, they will usually smell the lie and they are more likely to simply call out the hypocrisy and abandon that belief.

We can be nothing but a response to our environment which conditions our subjective experience and knowledge to which we are reflective in any capacity we gain, formative in our future knee-jerk reaction to the future present; determining the epigenetic expression of our genes manifesting conduct and identity for which we create meaning-making to reconcile a possibly locked in worldview which we have assimilated and progressed upon new information that fits like a puzzle piece into this worldview, a worldview which is formative of our adopted beliefs and values which are saliently operative in behavior and perspective, all the while working with the human condition and the desires and needs of the body inside pain/pleasure parameters. As we seek that which is pleasurable and avoid at nearly all costs true pain. Senseless acts of evil may be reduced and almost always found splayed in one or some of the following roots; selfishness, pride and inadequacy, desire and a lust for power, fear, depraved justice due to moral disgust, catharsis, dehumanization and the void of discontent due to unmet need.

How do you define a "belief system?" Are you talking about religious faith?

Everyone develops a set of beliefs. A lifelong Democrat, I believe in equal rights, women's rights, minority rights, protecting the environment, and good education and health care for all.