...a couple with limited church connections (either they went as kids, or their parents want a church wedding, or grandma said no place in the will without a church service) who are not members of a faith community. You have essentially a private service, no one from the parish shows up (except to clean up afterwards). At the rehersal there is always at least a few hangers-on that sit in the back row and snicker. Sometimes they are indifferent as to what readings are picked and communion is never included (usually because of the extra 45 minutes).
I wonder why we, as the church, support the second type of service. You can raise an argument that it is a form of evangelism, or that we should not withhold the sacraments from those who request them, but it still flies in the face of who we are called to be as church.
A marriage service in community draws the faith family around the new couple to support them in life and with prayer. The transition to married life is developed and occurs within the "faith village" where it is then nurtured. The union of man and woman is mirrored in the union of Christ with the community through communion. The marriage of people mirrors Christ's mystical marriage to the church, a marriage that is realized in the communion service.
Holding a wedding for the unchurched, who are not members of your community, violates the beautiful relationship between the mystical reality and the liturgical realization of that reality. It turns the sacrament of marriage into a fancy 'justice of the peace' event.
I used to justify this to myself by saying, "At least I have some contact with the unchurched, so this is evangelism" or "I can not know how God will work in their lives, and I do not want to be the agent of turning them away from the church." The arguments are all hollow...