"If you want to make sure that your successor doesn't preach the Gospel, Just admit lots of people into the membership who aren't truly converted."
Mark Dever - "False Conversions: The Suicide Of The Church" at 2012 T4G
In the same address Mark explains why it is important to guard your church against false teachers. There is a symbiotic relationship in the church, between false teachers and false converts. "False teachers produce false converts; false converts hire false teachers."
That would explain how it is that some fundamental, doctrinally sound, bible believing churches that I have known, have drastically degenerated in just one generation.