The problem is not church and state; the problem is a misapplication of the concept.
We’ll specifically speak about the Catholic Church, since I am quite sure this is what your reference was meant to focus on. When we, as people or as governments, try to operate lives which separate faith from reason, we get tyranny. The state is better at handling matters secular, and the Church is better at handling matters spiritual.
“Render therefore to Caesar the things that are Caesar’s: and to God the things that are God’s.” But never should church and state work against one another, which is what happens when secular life rejects the unwritten natural laws of God. The founders of the United States understood this when they spoke of our Creator giving mankind certain unalienable rights. The state has no right to contradict the eternal laws which God has declared since the beginning. So, when Christ’s Church speaks and the government listens, people demand a “separation of church and state.”
That way, we can enjoy “constitutionally-guaranteed rights” such as contraception, prostitution, in vitro fertilization, homosexual marriage, etc. It is this making religion a personal matter to be lived at home and never in public that creates such a problem today. A nation that embraces the will of God would not be engaged in prostitution, the drug trade, addictions, marital infidelity, unwanted pregnancies, crime, murder, rape, etc. A nation determined to fix these problems would not attempt to keep God out of the solution; logical solutions depend on a people determined to live a better life and to not lower themselves into the desperate world of crime and corruption that so many seem to believe is the solution to their problems.
Christ allows nations to rise and fall. Christ should never be banned from our solutions. And a final reminder: Christianity is not a democracy: Christ is a King. Always has been, always will be. What we think we deserve as a right, in the end, doesn’t matter. If we were to only treat others as we want to be treated, and loved God with all our heart, strength, and mind, we’d be much better off.
Hillsborough, New Jersey