If we love our neighbor and enemy as ourselves, through spirit and grace, we have exercised all that is due to any government. “Our citizenship is in heaven.” (Philippians 3:20)

This is the spoiler: The way of Christ and naturally the follower of Christ is radically different than conventional wisdom and contrary to worldly values. Always.

To say the pledge of Allegiance is anti-Christian. Let's examine the major points of it by definitions:
Pledge: To offer or guarantee by a solemn binding promise, similar to an oath.
Allegiance: [1] the loyalty of a citizen to his or her government or of a subject to his or her sovereign. [2] loyalty or devotion to some person, group, cause, or the like.
F**g:  A usually rectangular piece of fabric of distinctive design that is used as a symbol.(In this case, a symbol for the Republic of the United States of America.)

From these definitions we can understand a couple of things. Making a pledge is basically the same thing as an oath. And, giving your allegiance to something or someone is basically committing your loyalty to that entity. Also, the f**g stands for something more than itself. It stands for the country/government it belongs to. In short, to pledge your allegiance to the f**g means that you are making an oath of loyalty to the country, the United States of America.

#1 Jesus directly and without any qualifiers condemns making an oath to anything for any reason.
“You have heard that it was said to the people long ago, ‘Do not break your oath, but fulfill to the Lord the vows you have made.’  BUT I TELL YOU, DO NOT SWEAR AN OATH AT ALL: either by heaven, for it is God’s throne; or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King. And do not swear by your head, for you cannot make even one hair white or black. All you need to say is simply ‘Yes’ or ‘No’; anything beyond this comes from the evil one.” (Matthew 5:33-37)

#2 Jesus also teaches that men cannot serve two masters at the same time.

“No one can serve two masters. Either you will h**e the one and love the other, or you will be dev**ed to the one and despise the other.” (Matthew 6:24)

We can’t give our loyalty to two masters and be pleasing to both. Whether the choice is between God and money, God and man, God and a government or nation, the choice is always the same, one or the other. It seems that Jesus is saying ‘you can’t have your cake and eat it too’. In light of this it just doesn’t seem possible to me to give my loyalty to God, and then try and give it to a government at the same time. Jesus also said ” My kingdom is not of this world”. Jesus has a kingdom, and just like an earthly kingdom , I can’t be loyal to two kingdoms at once. It would be impossible to be loyal to the USA and Iran at the same time! It’s the same with being part of the kingdom of God. Jesus calls us to be loyal to his kingdom, and if we have given our loyalty to God’s kingdom, how then can we try and give it to America or any other worldly kingdom?

Supplement on Worldliness covering patriotism and love of country:
James 4:4 You adulteresses, do you not know that friendship with the world is hostility toward God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God.

1 John 2:15-16 Do not love the world nor the things in the world. If anyone loves the world, the love of the Father is not in him. For all that is in the world, the lust of the flesh and the lust of the eyes and the boastful p***e of life, is not from the Father, but is from the world.

Romans 12:2 And do not be conformed to this world, but be t***sformed by the renewing of your mind, so that you may prove what the will of God is, that which is good and acceptable and perfect.