Buddhist heretics?
While the Buddha was alive he had heretics. One was Yamaka who strongly believed that one whose taints are destroyed is annihilated and perishes with the breakup of the body and does not exist beyond death (param marana). Then there was the heresy of Sati. Sati believed that consciousness is autonomous and thus transmigrates unchanged (anaa).
I am sure there were other less known heresies mainly put forth by those who didnt fully understand the Buddhas teaching.
Today, we dont like to use the word heresy. It brings up extremely negative mental images. Some of us might recall the horrible deeds of the Catholic Church that when they executed a heretic, such as a witch, for example, they might first strangle her then tie her body to a stake and set it afire.
Buddhist heresy is quite different. The Buddhist heretic was one who harbors and spreads an evil wrong view (ditthi ppika/ppakam ditthigatam) which had the power to mislead one on the noble path. Because of being misled, the adept cannot attain nirvana. It would be, in fact, impossible. From the Buddha's perspective there is no wiggle room. The noble path is straight and narrow. Being nice and cheerful or working for world peace do not get one to yonder shore of nirvana. But these are not heresies. They only become such when someone believes that taking in stray cats, for example, is nirvana or more apt, If you live with a difficult person, thats nirvana (this was said by the late Zen master Joko Beck).
Today we still have Buddhist heretics although we arent supposed to call them that. What they put forth as Buddhism aint real Buddhism. If one were to follow the path these heretics have laid out they wouldnt reach nirvana. To provide one popular example of a modern heresy, besides Joko Becks nirvana, it has to be the view that just sitting (J., shikantaza) is synonymous with Buddhahood.
