I see two reasons which stand out:
1.) The love and desire to serve God in their own way as guaranteed in the Constitution.
2.} The love of liberty and freedom from oppressive government.
These are two things which do not come naturally for northerners.
The Constitution is a completely secular document. It is often criticised on that basis. There is no guarantee of worship or service to God in the Constitution. There is a little concept called the separation of church and state at work.
As I often point out, ignorance is the hallmark of the CSA apologists.
Don't worry, many of your fellow travellers will nod sagely when they read your post.
Walt