Semi-agree, but I think there are 2 fundamental differences between established religions and cults:

1. Complete shunning of non-cult members, and even harsher shunning of ex-members. This one may be a gray area, as certainly many religions identify all members of other religions as "going to hell", and I know Mormons who have been excommunicated for being gay. Still, the level of ostracism in mainstream religions is nothing compared to, for example, what happens if you try to leave Scientology. Scientologists declare you a "subversive person", stalk you, and essentially try to ruin you. I know many folks who have left the Catholic church, but in all honestly the Catholic church still tries to welcome them back with open arms.

2. Be secretive about the details of the cult before you are "bought in". Say what you will about organized religion, but it's pretty trivial to get the full text of the Bible, Koran, and other religious writings. Meanwhile, Scientology requires you to pay thousands and thousands of dollars to slowly get access to their screeds, and they have gone after ex-members who have attempted to publish this information.

These have nothing to do with being "established religions." As you said, Mormons shun. Many Muslim groups advocate killing apostates. It might be trivial to get a copy of the Bible, but the vast majority of how e.g. the Catholic Church runs is not drawn from the Bible using the most obvious interpretation, and is not shared with laymen - the Bible is not an IKEA instruction manual.

Also Mormonism is not particularly old. Mainstream evangelical/charismatic Protestantism was formed completely from storefront Pentecostalism in the early part of the 20c, making it barely older than Scientology or even the Nation of Islam. Scientology isn't bad because it's not "established," it's bad because it hurts people.

Mormonism is in a transitionary phase between Scientology and more established religions. It is taken seriously but still has a aura of non-seriousness about it. Scientology will probably reach that stage once it matures, but it will take a few generations still.

> Still, the level of ostracism in mainstream religions is nothing compared to, for example, what happens if you try to leave Scientology.

Worldwide, a majority of muslims support the idea of a death penalty for apostasy (renouncing the religion).

Defining a cult is a lot harder than it sounds at first glance. My personal definition, which is not very useful since it's so subjective, is "A cult is a new religion formed on purpose by a charismatic person who is knowingly lying in order to gain temporal power."

seems odd to not acknowledge how the non-secretive nature of modern christian religion is such a recent (technological and social) development and still holds some fringe controversy at similar levels as these other extreme cults

Yes in the sense that all religion has a dose of magical thinking, but not in the sense that cults are a specific set of practices that set them aside from mainstream religion.

Shunning of members, cutting ties to non-cult people, taking over the finances of their members (and forcing them to donate).

There are some gray areas and some mainstream congregations can cross into cult-like behavior, but in general, there is a demarcation.