The true church doctrine should always be the Bible. Christians should stick to the Bible. Josh is refering to people who clearly 'fail to see' a part of scripture. I see this as the worst thing in Christianity. For if you fail to believe or apply one section of scripture, it is quite possible that your whole Christian 'life' will crumble. All of church doctrine (true and false) have connections to salvation. What is frustrating Josh, is when some self-proclaimed Christian says he or she whole-heartedly believes something completely opposite to what the Bible says, and then the church is forced to accept this because they don't want to say the truth because it might make some people leave the church.
In the case of someone proclaiming a doctrine that is clearly contrary to what the scriptures teach (though again, this is a grey area, since (for example) Josh probably considers free will to be contrary to what the scriptures teach...), I think the church should gently and lovingly correct that person. Just because I don't think churches should be autocratic about doctrine doesn't mean I'm advocating the touchy-feely religious pluralism you see in too many 'liberal' churches today...
Now on the more specific front, I don't believe that freewill and predestination needs to create separate churches. I believe we have freewill in deciding whether we will follow God's predestined plan for us. God knows what we choose in advance so he knows whether we will follow His will or not. Freewill and predestination are both comforting thoughts; we have some purpose while still having a powerful God ruling over us.
I've tried to keep the free will/predestination debate out of this conversation, since I'm not sure that dead horse needs any more flogging.
Yet when it comes to determining sin, doctrine must be set. The unwillingness to say, "I have sinned and with God's help may I never do it again," with many wrongs such as abortion, immoral sexual conduct, and other controversial sins is unacceptable within a church. To say 'wrong is right' is really what confuses the non-Christian.
We are all sinners, so if we kicked all the sinners out of the church, there wouldn't be anyone left! I agree that flagrant, unrepentant sinners can be damaging to the body of Christ, but why is it that only controversial sins are unnacceptable?