I don't know if it is the biggest threat, but I see flag idolatry as a major problem in the church. Many (Most?) Christians get way more upset at disrespect of the flag or failing to say the pledge than they do over someone using the Lord's name in vain or damaging a Bible.

I've come to the conclusion that saying the Pledge of Allegiance is sin and idolatry. We are told we can't serve to masters, so how can a Christian honestly pledge allegiance to the flag and to God? As the US government becomes more and more anti-God, this becomes more obvious than it used to be.