Deanna Laney, religion and why secularism works

I was discussing this case with my ever-witty boyfriend, and he made a great point: How is it that we know that God wasn't actually talking to her?
It was a joke but it goes right to the heart of the questions of knowledge and how that affects church and state. There is no actual way to prove or disprove God. There is no way to prove or disprove that God spoke to any one person. There is no way to prove or disprove that God wants any one thing. That he is telling women to kill their children is as testable a hypothesis as proving that he spoke to Moses out of a burning bush, which is to say, it's not at all. In fact, that is the very notion of faith, that one believes without proof.
The only test of religious revelations is to run them by the argument by authority. In a religious institution, we sort of arbitrarily decide who are the gatekeepers of religious revelation and they are accorded a position of superiority over all others. For example, in the Catholic Church, people don't get to decide what is a miracle, whether they witnessed it or not. All miracles have to be verified by the Church authorities. Who made them authorities? Anyone can see how no matter how long and hard you dig, eventually religion is based on faith and authority, both of which are ultimately arbitrary.
In a democracy, everyone is equal before the law, meaning no one person legally has more authority than another. There is no trump card--one person legally can't come in and be believed over another due to a higher social position. So we must base our decisions on the facts at hand. That science is perfectly suited to our legal system has been a great boon to humanity.
So, how do we know if God actually told her to kill her children? We can't know so it's not admissible in court. We can only judge what she did (kill her children) and whether or not she was of a rational mind when she did it. Since she was beholden to voice in her head that told her to do it and she was unable to resist that voice, she is judged not to be in control of her actions at the time. Whether or not the voice was actually God or not is irrelevant; what is relevant is whether or not she was able to defy that voice or not.
If we lived under a theocratic government, that is, one where powers were based on religious authority, her trial would have been much different. The debate would not be on whether or not the evidence shows that she was unable to think clearly at the time of her crimes. The debate would be authority-centered. Simply put, the debate would be about whether or not God actually told her to kill her children. The prosecution would argue that the Bible forbids murder, particularly infanticide. The defense would bring up the story of how Abraham was instructed to kill Isaac but God stayed his hand at the last moment; perhaps her hand was not stayed. The jury would decide according to which side demonstrated better Biblical authority.
I hope it's clear why our system is a better bet. If you were charged with a crime, which court would you rather sit in? And of course, in a religious system, things that don't exist in a factual sense but do under certain belief systems can be crimes, like witchcraft.
It expands beyond the justice system. Policy decisions need to appeal to reason, not authority, because there is no ultimate authority when the people own the government. What's nice about the reasonable approach is that it has science at its disposal for use. Policies can be tested and disposed if they are ineffective by the scientific method. Under the religious system, a policy that is causing problems cannot be changed. If God is perfect and he handed down this law, who are we to say it doesn't work? Under the secular system, we are free to tinker and life demonstrably improves.
Leaders have a job and they are beholden to do the job they were hired to do. Under a democratic system, they are elected and are beholden to the populace who elected them. Under a theocracy, leaders are appointed by an ultimately arbitrary system of authority. They tell everyone else what God wants and there is no way to prove or disprove this, so you must simply live with it. If you are the sort of person God has a problem with, you are in big trouble and no amount of reason is going to save you. While we still presumably have a democratic system where our President was elected (at least legally), he has publically declared that he considers himself appointed by God. If he believes this, he does not believe that he is beholden to the people he elected. Something to consider.