The answer to your question is very simple: Because a law is not supposed to “promote what is good and right”. The purpose of the government is not to make people better people. If you firmly believed that the purpose of government was to make people better people, then the logical conclusion would be to support an absolute monarchy with as extensive a feudal system as possible and strict rules for The Powers That Be. In Christian ethics, humility is, of course, one of the greatest virtues. To promote it is to promote what is good and right.

There is no system of government that better promotes humility than one in which the most people are subjected to rule which they cannot overturn and which they must either serve humbly or hate spitefully; this would, of course, provide the ultimate promotion of comportment that is good and just. By this system, you would find more and more people turning to the Father of Lights to light them afire with love and strength to do their duties, because there is no other relief; this happened in the Middle Ages and beyond. The select few who were in charge would, of course, be subject to many strong temptations, but by enforcing strong legislation this could make them better people also; the absolute monarch himself might have to suffer by notbeing made more moral himself, but this is, of course, a small price to pay if our goal is indeed promoting as much “good and right” as possible.

But I doubt you support fiefdoms, absolute monarchy, or slavery. Therefore you do not really think the purpose of government to “promote what is good and right” and establish “moral laws”, if that means laws that will make people good people.

I believe, and suspect most of you believe, that the purpose of a government is to promote or allow good moments: a couple on a date at a restaurant, a kid on rollerblades in the park, two friends out fishing on the river, a bookworm curled up by the winter fire. All our wars, all our taxes, all our elections are in vain if they’re not aiming at this. This is why we ban murder and allow people to lie. This is why we make theft illegal and civilly turn a blind eye to unforgiveness. This is the real deal: something good and thick to aim at promoting.

You have asked, Why we do not support what is right when we have an opportunity to do so. The answer is, We ought to; but with what means we do it is the question. You do not, I imagine, think we ought to create a secret police to force everyone to be moral at gunpoint; that is a misuse of power. Is it proper to support what is right with a government also?

No, it isn’t, because the reason behind having a government is damage control and protecting moments where good things can happen; it is not assuring piety itself. We do not actually believe that is why governments exist. If they exist to promote equitable distribution of power, as in Reinhold Niebuhr, that is not because equitable distribution of power is itself the Good. It is not; the universe is set up like a complicated and divine monarchy, not a democracy. Equitable distribution of power is a means to getting Johnny to grow up to love watching a sunset, reading Chaucer, playing football, or eating a fudge sundae. It is, in effect, to let him be fully human, not to make him a good human. It is to prevent what Coleridge records,

O grief— but farewell, Love! I will go play me
With thoughts that please me less and less betray me.

Theft, murder, and the like are the prime enemies of this; that is why we think they ought to be removed, not because we think them wrong. Our moral judgments have nothing to do with why we support legislation, except by what is, in logic, an “accident”.

This is why I believe in democracy, even though I observe that monarchy itself is a very good thing; monarchy is the foundation of the universe. I do not believe in democratic action because I think everybody good enough to have a say. I believe in it because I don’t think anybody good enough to have unrestrained power. I believe in it because it is damage control and will hinder those moments that destroy Johnny’s love of nature, poetry, food, games, music, and all the other good things of this world—this were-eald, this Man’s Age.

This is why I support legislation on slander and copyright but draw the line at lying and fornication. A secret police itself may act immorally, but the legislation that creates one is not immoral because secret police are bad; it is immoral because it is a lie against what we believe a government exists for. To live in fear of losing your store will not help your leisure time to become holier. To worry that you might be shot dead tomorrow cannot help you love your wife better.