Here is a great summary of the duty of the state in relation to the Church given by a great priest who shall remain anonymous.
Look.. it's perfectly simple...
1. All men have duty to worship the True God.
2. The State is a collection of men
3. Ergo, the State has the duty to provide for the worship the True God.
1. Not all men recognize the True God and therefore don't worship Him.
2. But worship must be both interior and exterior in order to be an act of true worship, and since no one has the ability to coerce another to make an interior act.
3. Ergo, the State cannot coerce men to worship the True God against their will.
1. The State has the duty to provide for the common Good.
2. False worship of false Gods and especially Satanic worship mitigate against the common Good.
3. Ergo, the State has the right to forbid false worship of false Gods especially Satanic worship.
The State must allow men to worship the True God ergo, the State cannot impinge or make laws regarding the Catholic Church which is the only true Church which gives true worship to the True God.
But, the State cannot force its citizens to engage in worship, ergo, it cannot mandate that all be Catholic or attend Catholic worship services.
However, the State CAN and SHOULD both foster evangelization programs that promote the Catholic Church and forbid the exercise and promulgation of false religions.