I ran across this article tonight. I think it has some very helpful tips for discussions amongst Catholics (and other Christians, too).
10 rules for handling disagreement like a Christian, by Bishop Allen H. Vigneron :
All too often we fail to treat each other with either the seriousness or the charity which our common Faith deserves. We ignore to our eternal peril the one prayer request of our Lord on the night before he died, that we might all be one in truth.
Lord, forgive us for breaking your Body into little kingdoms where our will can be done. Make us one in You once again.