All laws should only be based on protecting the three natural rights.

Prohibiting homosexual marriage isn’t based on those, but then, neither is the involvement of Government in the heterosexual marriage.

Isn’t popularity the only difference between a “universal moral code” and a “personal moral code”? How would you propose differentiating this from tyranny by the majority?

It seems to me that there should be a definite distinction between universal moral codes and personal moral codes. Since everyone agrees on the right to life, then it follows that laws against taking away that right–murder–are based on the universal moral code. Same with liberty and property (although I realize that most people don’t understand property rights anymore). So, I am going to define universal morality as only pertaining to those three natural rights. Violate those rights, and you have broken the universal moral code.

When you come to things like infidelity, homosexuality, etc., how can you justify legislating them? If they are not violating someone’s rights, they are not violating the universal moral code. Instead, they are violating personal moral codes–and whether or not those personal moral codes are held by the majority of the population seems irrelevant to me. If laws are based on personal moral codes, how can they be legitimate? It seems that then it is just democratic ruling instead of protecting the rights of the individual.

I think our disconnect is about the role of economics. You seem to be suggesting that economics reveals morality. I think instead that economic arguments simply link laws to moral justifications. As illustration, notice that each of your examples implies a moral judgment: costs of harm should be born by the party who caused the harm. The normative “should” reveals that the statement is a moral judgment. To me it seems that economics is a tool for achieving desired results, but moral judgments dictate what economics is used to achieve.

Another way of putting this is to say that judgments about what amounts to a negative externality are always moral judgments.

I’m curious about your rule that “To the extent morality reflects some sort of harm or benefit, which society is willing to recognize, conferred on an unknowing/unwilling participant, I think it is a good basis for law.” It seems like you are proposing that rights should be defined by majority vote. What limits if any would you propose to limit this?

Anyhow, I think a lot of the public sense of morality comes from an economic idea. Adultery is immoral because it causes emotional harm to people who didn’t make the decision to commit adultery – e.g. children or a cheated-on spouse. Violence is immoral because the injuries are not born in proportion to responsibility for the fight.

May laws attempt to internalize externalities – positive or negative. Murder is bad because the cost isn’t born by the murderer. Ditto for most other criminal laws. Other laws try to internalize positive externalities, often by redefining property rights to be commensurate with the benefits/costs the property creates. Intellectual property rights are a good example of this.

Changes in social values or technology will shift where we perceive harm/benefits to accrue. For example, we may decide that having a daughter marry someone of a different race isn’t such a harm, and miscegeny laws no longer make sense. Or perhaps the internet’s ability spread content makes copyrighted material more valuable, so we need to expand copyright protection.

In cases where the external harm/benefit is harder to see, some people have tried to show a link between activities traditionally looked at with moral disdain – strip clubs, prostitution, pornography, etc – and a negative externality. The Broken Windows theory is an example of the argument linking immoral activity with a negative externality. I don’t know that a similar argument can be persuasively made about same-sex marriage.

To the extent morality reflects some sort of harm or benefit, which society is willing to recognize, conferred on an unknowing/unwilling participant, I think it is a good basis for law. To the extent a moral reflects some cost/benefit that society is not willing to recognize, then I don’t think that moral is a good basis for governance.

More importantly, government gains legitimacy from its people. Since voters have repeatedly passed same-sex marriage prohibitions, it would be exceptionally undemocratic to contravene the people’s will in this matter.