You wrote:
"So let me throw this in the mix... suppose this church wanted to minister to your youth, what then? They wanted to host events and what-not and use it as an outreach to other churches, and to the community.
Does that change anyone's thoughts on separation from them?"
You've focused the question, so I'll try to focus an answer.
I think a valuable insight and distinction may be gained from our Lord's instruction to John and the rest of his disciples in Mark chapter 9:
"And John answered him, saying, Master, we saw one casting out devils in thy name, and he followeth not us: and we forbad him, because he followeth not us.
But Jesus said, Forbid him not: for there is no man which shall do a miracle in my name, that can lightly speak evil of me.
For he that is not against us is on our part." Mark 9:38-40
I think the things to take out of this are:
1. John saw other "Christians" who (as he saw it), didn't believe and do things "correctly" (i.e. they weren't following Jesus closely, like the apostles were.)
2. Our Lord confirmed that God was indeed still working through them nonetheless, saying they did "real" miracles. (i.e., We might say today, “people were really getting "saved" through their ministry.”)
3. Our Lord confirmed that it was not His will that such should be hindered. (A powerful indictment against the antichrist spirit infecting the Church that persecutes those with different opinions.)
4. Jesus did not say, however, to give up the truth that you know and go and join them in their error. (No, follow the Lord as closely as you can, according to the light you’ve been given.)
As individual Christians therefore, we must follow the Lord with all our heart, soul, mind, and strength, while still patiently loving our neighbor as ourselves.
For instance:
If there is "real" fruit in another's ministry, do not hinder the work; God in His mercy has put the brother on the same Path you are on. Just pray for God to continue the work; and pray for what you know he lacks. (Just as we hope others, further down that same Path, who see our faults, are praying for us...)
So:
The local Church, (as well as the individual for that matter), has the duty and responsibility to set some kind of guidelines of Truth: "Unless we can be shown from the Scriptures otherwise, we believe such and such things to be NECESSARILY true,...", etc.
Now, if a particular Church has come down on the side Eternal Punishment, for instance, they should not go and join in the work of those who "err" in this regard.
However, they should have large enough hearts to still pray that God, who is rich in mercy, would still mercifully bless the work, despite the secondary "errors" involved.
What do you think, Brothers?
Doug