If the false teachers in 1 Timothy 4 and 2 Timothy 4 were members of the local churches, could they not have been ex-communicated?

This text is from a transcript of a talk by David Gooding, entitled ‘An Abundant Entrance into the Eternal Kingdom’ (1985).

The answer to your question: 'could these men not have been ex-communicated', is, of course, they could have been. Perhaps the answer ought to be also, they should have been. But very often it happened that in the early churches there were some utter rogues, and the church was powerless to do anything with them. There was a certain Diotrephes, you remember, who not only wouldn't receive ordinary members and cast them out of the church, but he was for refusing access even to such a one as John the apostle. Now, John the apostle says, 'When I come, I'll deal with him', but it would appear from that context that there wasn't anybody locally who was able so to deal with him (see 3 John 1:9–10).

Similarly, Paul warns the elders at Ephesus that after his departure, grievous wolves would come. That is, the attacks on the church would arise from the inside (see Acts 20:29–30). How long they were allowed to remain inside, we are not told, of course; but the fact of history is that, alas, so very often false teachers and prophets have arisen up and sometimes they have dominated their church and many another church as well.