Has there ever been a systematic persecution of Buddhist heretics?
King Asoka liked the Dhamma so much that he lavished the monks with robes, food and medicine...

This attracted many fake monks...

Monks were beheaded in an effort to find the imposters but that didn't work.

They started the third council to purify the monastic order by questioning monks to find out who knew the Dhamma and who held heretical views so they could  expell the real imposters   from the Sangha.