We don't value religious liberty merely as an abstraction, but because it protects our ability to live out our faith at ground level; to serve others as we're called to do. Anthony Bosnick, Director of the Department for Charity and Justice at the Archdiocese of Washington, has an excellent piece in the Washington Post making this point.  Faith in action promotes the common good:

By giving witness to what their faith teaches, people of faith make great contributions to society through ministries such as food pantries and soup kitchens which serve the needy and vulnerable, clinics and hospitals ministering to those who cannot afford to pay, and schools educating young people who would otherwise attend schools that do not adequately meet their needs. Faith in the public square raises our awareness and concern for those in need, both at home and abroad. It helps to build community and promote the common good, enriching our lives and our communities and nation.

And religious liberty is essential to that effort:

Catholics are wary of the privatization of our own faith and the negative impact on society for all people of faith if we can no longer give public witness to what we believe. Our religious liberty gives us the freedom to live our faith in a public way, which we do -- not just through acts of worship, but also through loving, charitable service to others, which contributes to the common good . We serve not just Catholics, but everyone in need. This is part of what it means to be Catholic, and when our religious liberty is suppressed, this service to others – a very public expression of our faith – suffers.

This is the first in a series of three essays in the Post on faithful citizenship; looking forward to the others.