So Far As Possible
Those who are merely being antagonistic should just be avoided. I see this as the equivalent of Jesus telling the disciples that if they were not received in a town, to shake the dust off their feet. I do not think this should be done hastily, but if after repeated attempts to be civil have failed, the best option is to avoid the situation as much as possible. This assumes, of course, the other party is an unbeliever. As believers, we are called to reconcile our differences, if necessary seeking other believers as mediators.
The New Testament is also clear that those who seek to undermine the authority of the Scriptures, or to distort the gospel, cannot be left to promulgate their teaching in the church. Paul, in Galatians and the Pastorals especially, makes it clear that false teaching of this type requires swift and decisive action.
But what about those who hold the Scriptures in high regard, and are sound on the gospel, but hold to some doctrine that we feel is contrary to Scripture. Should those who hold to infant baptism have discourse with one who believes in believer's baptism? Should one who holds to a day-age view of creation be shunned by those who believe in literal 24 hour days? Individual lines are always difficult to draw. What may be a major doctrinal point for you may not be for me.
In my opinion, those who hold to certain essentials should be treated as brothers. In non-essentials, we should be able to openly disagree without dividing. Being at peace with someone should not exclude us from having spirited (Spirited?) discussions about doctrine. In fact, it should encourage it. Our unity in essentials should free us to discuss our differences in substantial matters that are not essentials. I have benefited from interacting with and reading those with whom I have some fairly significant differences.
I am a fallen creature, and as such I know that my doctrine is not now perfect. Therefore I have to be open to the possibility of change. At the same time, I have centuries of discussion on critical doctrines where other redeemed men have been united on key doctrines that they have found in the Bible. I cannot in good conscience set those aside because of a contemporary mood that finds them distasteful.
Therefore, so far as I am able, I will live peaceably with all. But I will also heed the call to contend earnestly for the faith once for all delivered to the saints.
Addendum (Monday, May 7 at ~ 8:30 EST): Reading through this again, I want to emphasize that the ending is not intended too mitigate the beginning of the series. There are only a few doctrines for which I see us being called to contend earnestly. While I don't see these doctrines as being limited to either the Apostles Creed or the Nicene Creed, they are definitely good starting points. I would quickly add the inspiration and authority of Scripture. I would not include, for example, the mode and timing of Baptism, which I see as important and worth discussion, but discussion that first and foremost acknowledges the bond of Christ. This does not mean that I would expect an expressly paedobaptistic congregation to accept me into leadership (I would, in fact, expect the opposite). But I would expect that we could fellowship and grow together in the knowledge of our Lord and Savior Jesus Christ. I also believe in that situation I have an obligation to not make baptism a subject of discussion. (As a sidenote, it is generally much easier for a Baptist to be accepted into a congregation of paedobaptists than vice versa.)
This is all to say that I think too many of us are too willing to divide over doctrines over which we should not be dividing. While some of them may lead us to be parts of different congregations, they should not prevent us from having close friendships with one another as brothers and sisters in Christ. If it sounds like I've been listening to the Together for the Gospel guys again, I have.