There's huge difference in Christian theology that goes unreported.  

I for one stand with those who do not believe God cares about nations or, structures that separate humans into often waring tribes.   There are no national flags in my church, nor would they be appropriate.   A nation, by definition, is concerned first by its own survival, or maybe domination based on self-righteous justification.    That has nothing to do with a universal God who sees unity, not separation by politics.

When we combine the symbols of a nation with the symbols of a universal deity, neither is well served.   In particular it belittles the symbolism of a loving God who's 'kingdom' has no concern for national borders. 

*This is my opinion and does not represent the opinion of all Christians.    I do not claim any special 'gift' of truth.  I have actively pursued a spiritual component to my life that fits comfortably with both my head and heart.

It's a choice.