You said -There is in many areas such as marriage and driving.
Do you think Alabama is going to recognize a Mass. same sex marriage? If two gays "married" in Mass. move to Alabama, do you think AL is going to recognize it for state income tax purposes? Or probate? I don't think so.
'bama would recognize a hetero marriage from another state. Like any system, reciprocity will face challenges from idiots like the Mass Supreme Court from time to time.