Side of God means that you are on God’s side. Our merch is for people who are on His side and strive to build His kingdom and fulfill His will, therefore they are Christians.
Because as the Bible says, you cannot serve two masters. Either your master is God, or it’s the world and the devil.
You shouldn’t interpret the meaning of the name SIDE OF GOD as “us vs. them” in regards to other people. We are here to love. God can forgive even those people who have done terrible things, just as He has forgiven you. We are here to show the lost sheep that God’s side is the better side. To help them return to their rightful shepherd.