Where and when did this alleged "slaughter" take place? Give me dates and places. Tell me the names of some of the people involved.
The Albigenses were a people of the reformed religion
"Reformed religion"? Reformed Gnostic religion, maybe. They, unlike the Waldenses, were certainly not Christians of any stripe or kind. Your Baptist congregation would throw them out on their ear after they explained to you that bearing children trapped "good spirits" in "evil bodies," and so it was better to practice sexual perversions that didn't result in conception as well as ritual suicide.
those who did not join Constantine, the title of the edict is in this article
http://www.reformation.org/vatican-and-islam.html