Law of proportionate belief

Arnold Kling proposes his "Law of Proportionate Belief". Briefly stated, his law is that:

...one should believe in a certain proposition or policy prescription in proportion to the arguments for that position.

Well and good, and quite sensible.

But, as the old saying goes, the devil is in the details.

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The biggest detail has to do with how you count arguments. Is every argument as weighty as every other?

Consider the issue of gay marriage. I do not find the arguments either for or against gay marriage to be overwhelming. If I were forced to choose a position, I would favor allowing gay marriage, because my best guess is that two gays who choose to marry are not causing harm to anyone else.

However, there are some people who will argue that allowing gay marriage would be one of the worst travesties possible. And there are some people who will argue that not allowing gay marriage would be one of the worst travesties possible. My opinion is that both of those strong positions violate the Law of Proportionate Belief.

One argument holds that redefining marriage to allow same-sex marriages will have a corrosive effect on the family structure. Another is that it might promote more stable gay relationships.

It seems to me, you can't just count up the number of arguments someone might make for or against a position. You have to weigh them, and people will differ over how much weight to give any particular argument. What might appear to be arrogance to one person might be a very high weight assigned to a particular argument–with or without good reason–by another.