well, there's the practical side, and there's the emotional side.
for some people, the romance of a public commitment, marking a decision in front of everyone etc is important. for others it isn't. I don't see any right or wrong about that, it's up to each couple to define the state of their relationship.
then there's the practical side - houses, money, raising kids etc. at the moment, there are assumptions in law about the differences between marriage & co-habiting (or just being a couple, with separate homes).
Perhaps if the practical side wasn't linked to the romantic emotions, it would be easier? So couples could get a 'commitment package' from a solicitor, that sorted out the legal side. If they then wanted to do a big party and/or church ceremony, that would be their own choice. If the ceremony did NOT automatically involve the commitment, and people still had to do that anyway, then it would perhaps make them think about WHY they wanted the marriage in the first place.
and if you KNEW that there was no financial responsibility towards each other until the 'commitment pack' had been signed, then maybe, just maybe, it would make people be honest about how committed their relationship is before they have kids. (I would expect there to automatically be responsibility towards children, no matter what the state of the adult relationship)