These guys were more moderate than most Muslims. The first pillar of Islam is "There is no God but Allah, and Mohammed is his servant. Anyone who says otherwise is an apostate. The penalty for being an apostate is death. I'm not sure who carries out the sentence, perhaps any follower of the prophet Mohammed.
The preachers are to be commended for having the courage to speak out. Most preachers today are timid when it comes to stepping outside their comfort zone.
Apostacy implies rejection of a former belief. Only someone who has professed to be a Muslim can be a Muslim apostate.