The foundation for healthy interpersonal relationships seems deeply tied into the core values of (some) "restrictive religious ways". "Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres." I would posit that the closer people walk to those ideals, the healthier their society will be.
That said, Christians, in general, would agree with you that law by its very nature has no power to bring about good in people. That's pretty much one of the core tenets. In the end, laws serve only like the double yellow line in the middle of American highways. It's a guide that helps us share the road without hurting others.
The guard rails of commitment, love and genuine care for others brings about an environment where relationships can flourish. They provide stability and care that children need to thrive emotionally. They keep us from swerving into relational "oncoming traffic" when we get frustrated or angry, instead encouraging us to stay in the lane and figure out how to work together.