All Jedi beliefs (religion) of the force and use of it spawned many Millennia ago. The present Jedi Academy infuses their age-old beliefs, that all and every practicing Siths and factions are a danger to the galaxy. Dangerous to the stability of the Republic Central Government.
This belief came about many Millennia ago with the Jedi’s experiences with an extreme sith order; The Serpent Order (or Ring). The Serpent Order was an extreme order and a very secretive one from the start. (see; Sith vs. Sith)
This Extreme Sith Order had no home world or rooted deep in any one system. The Serpent Order (Ring) were extremely dangerous influential Siths, with the highest caliber of cunning. Not much is still know about them, their numbers, or exactly when they originated. What is known of them is that they are long term influential manipulators. Their goal is full system domination and the destruction of The Jedi Order.
One such example of a Serpent Sith is The Emperor Palpatine… His profile showed all indication of this extreme order. This ideal Serpent Sith has no bonds with his birth world and would have destroyed it to meet his goals. His long term plan and manipulation of systems/worlds to gain ultimate control is The Serpent Ring’s primary objective.
They (Serpent Order) are full masters of their craft, and easily move about, in both Sith and Jedi Orders, without exposing their true nature or identity. No Serpent Sith has ever been documented in the use of their force abilities. As those that do witness… always perish. This is one major reason, why the Jedi have taken up a policy of condemning all Sith religions.
The Jedi themselves cannot sense or flush out any Serpent Master and thus, all Siths and factions of Siths are considered dangerous and a threat. The Jedi have instilled (infused) this (fear) knowledge to all their Padawans from early training on to their final seat at the Jedi Council. ( Qui Gon Jin, may have had a different view. This may be why this great Jedi was not on the Jedi Council?).
Jedi law (if there is one) mandates, extreme prejudice on all Sith Orders and factions. All existing records and documentation, concerning Siths, are mirrored in their belief that all Sith Orders are possible Serpent Sith Orders. Therefore, all Sith Orders must all be terminated and not allowed to rise again.
For a Millennia since the Jedi believed they purged out all Siths, that they have been extinct. The remaining Sith Orders, including the Serpent Ring had taken to master their craft (religion) underground. The Sith Orders had been weakened but not extinct, as the Jedi have so believed.
A thousand years have passed since the Sith were believed to be extinct, by the Jedi. Through this time the Jedi have become complicit in their thousand-year rule (with the Republic).
Now the time for awakening has come. With the Serpent Ring’s rise to ultimate power in the galaxy (Palpatine), all systems and worlds are threatened. Many of the hidden Sith Orders have once again Risen. (see: Sith vs. Sith).
NOTE: This is how Jerrid understands the history of Jedi/Sith religions. His Order follows “The True Church”, and “The True Teachings”, which originated a long time ago on Othala. Before his people were conquered, displaced and forgotten by the Jedi/Republic. A Millennia past…