Keeping Your Temper in Religious Debates
How does one deal with religious debates without getting angry?
When you speak with people about God and his revelation, you are working for their salvation and happiness, and this means that you love them. So loving the ones we speak with is the best way not to give in to anger. Better to be angry at the devil, the deceiver, than at the poor souls who labor under various errors. You should see yourself as helping the Good Shepherd to bring back his lost sheep, not as an opponent or accuser.
Pray for the ones with whom you speak before, during, and after your talking. Ask the Lord to give them all he desires for them and to use you as his humble and peaceful instrument. Then you will be imitating Christ and the apostles, and then, if anger against evil is warranted, it will be appropriately expressed and won't be a general attitude.