Freemasonry is a secret society.
All secret societies are satanic.
Freemasonry is the most well known secret society.
Freemasonry itself is a satanic organization, even if some of the Freemasons seem otherwise like "good guys."
Here is an overview of Freemasonry:
Secret Societies aren't inherently Satanic, but they are predisposed to fall to Satanism.
Anything done in secret eventually gets taken over by Evil in secret. With no one having the knowledge to stop the corruption, how could you possibly hope to persist when so many wish to take over your organization and steer it off a cliff?
No... Secret Societies aren't Evil by nature, just like driving your car backwards isn't necessarily Evil. Sure, you might be able to get away with it for a while, and you might even be good at it, but eventually you'll crash ass-backwards.
If what you do has to be obscured from the masses, no matter if it is honestly altruistic or not, you're just begging for Satan to come along and take advantage of your pride.
As for Freemasonry in particular... All Secret Societies espouse the Hidden Truth of the world, otherwise people wouldn't see enough value to bother joining and doing all the weird rituals to begin with. They do, however, eventually pervert the Truth with lies and take advantage of the trust they build with their members.
TL;DR: Secret Societies don't have Checks and Balances because they are secretive. Therefore, they will always be completely vulnerable to corruption from within, and have no backing from The People to weed out said corruption.
Long ago, I joined Rosicrucians by mail. Their booklets taught witchcraft, even before I knew what witchcraft was. I stopped and threw the booklets in the garbage. It is not something to be messed with.
Did they actually teach witchcraft, or esoteric Christianity? Groups who taught of the spiritual gifts of Christianity have been persecuted throughout history. They were tortured, etc. This drove them underground to safeguard the Truth of Christianity.
Satanic groups calling themselves Christians have hidden this knowledge. This knowledge is what the world needs now. Fearing it is to play into their hands.
Esoteric Christianity is not Christianity. Those groups that you mentioned were persecuted because they taught “spiritualistic” practices that are not taught in Scripture, and 99% of the time this leads to Gnosticism, contact with demons, or general heresy.
The Bible contains everything you need regarding spiritual warfare. Appealing to external esoteric teachings is only going to bring trouble.
Everything in the Bible is esoteric. How do you think John saw what he saw?
Do you think you're not in contact with demons? Spirits interact with everyone and everything. Some people choose to be conscious of this and to face their demons.
The Bible is a very mysterious book. It teaches much more than people realize. You can't appeal to the Bible to back up your points without citing particular verses. Each verse can be taken many ways.
You mention heresy. It appears once in the KJV.
"But this I confess unto thee, that after the way which they call heresy, so worship I the God of my fathers, believing all things which are written in the law and in the prophets..."