but...but...it's not the real thing!

Congratulations! Your daughter is marrying her live-in boyfriend of several years.

However-they have decided that while they will have a full ceremony and vows, they will not sign any marriage certificates and thus not be legally recognized as a married couple in anything other than their church/religious beliefs/etc. Your state doesn't recognize common-law marriage, and there are no legal hurdles to them getting a civil marriage-they just don't want it and do not have any intention of changing this.

How do you react? Does your opinion change if it's a different church/religion than the one you follow?