Because people rule their life on base of beliefs, maybe ? (beliefs=unproven concepts assumed to be true)

If life is a formal system, then it needs postulates. Obviously humans can’t agree on postulates. Do you have a useful scheme of postulates that you’re sure all humans will agree on? If so, please share. You’ll be able to clear up tens of thousands of years of misunderstandings if so.

Is life a formal system ? I prefer to say that we need to make hypothesis, and this is part of life. But religion is not simply a collection of hypothesis.

In my view, religion is a cultural spine of a community that defines the rules for living together. It also comes with a set of assumptions (beliefs) that are used to justify the rules, make the whole hold together, and enforce their acceptance.

Calling back into question the assumptions lead to question the rules. This puts the community at risk. As a consequence religions establish protective measures. Some of them are swift and brutal. I hope you understand what I'm referring to.

Some religions are much less toxic, but there is still the problem of their assumptions that introduce a bias in the act and decision making. People who adhere to a religion tend to forget to put a weight of confidence in the assumptions with the rational to not put the community in danger. Anything that represent a threat to the religion is considered bad, and this includes calling back into question assumptions and rules.

Science did not work that way. And this is why it evolves so fast toward a better understanding of the world we are living in. I'm not saying science is a religion or an acceptable religion substitute. I'm just comparing the effectiveness and benefit of a faster evolution of knowledge.

I'm convinced by multiple personal experiences that any community (e.g. startups, forums) needs a cultural spine and community rules, but I don't think that religions is the appropriate answer to it. The rule and the knowledge must be able to evolve and this is only possible when they can be called back in question by anyone anytime, and an objective method is used to decide. Assumptions and beliefs should be considered as mere hypothesis. Religions tend to obstruct evolution for their survival and the survival of the community. And of course many humans use religions as leverage to manipulate people, not only for the good of the community.

The real problem of religions are their beliefs that we can't call back into question. People brain washed through all their childhood with these beliefs, that we are requested to respect, can't make the difference with was is true and not, can't call back into question the beliefs and are prone to integrate similar irrational beliefs. This put humanity at risk.

That is a summary of my current view of religions. Note that it may still evolve because it is only based on my current knowledge and past experience.

What specific Buddhists beliefs suck, or are unproven?

reincarnation ?

That's a misrepresentation of Buddhist beliefs. The whole reincarnation thing is a teaching about karma than a literal belief that you will come back as a bedbug if you're naughty.

Anything else?

Why do you think Buddhism is so much better?

Off-topic: because the Buddha explicitly favours reason and testability over blind belief. Granted most Buddhists have developed rituals akin to other religions over the millennia (and also a lot of mythology that demands blind belief), but core Buddhism (as given in the suttas) is almost not a religion. In fact calling it a philosophy of life is a better description.

I would define Buddhism as: A form of introspective psychology.

Buddhism makes testable predictions about mental states and proposes systematic mental exercises to test those predictions.