Don't you realize that this creates an opportunity cost every time someone decides to vote?

I do. But your statement is not always true. For instance, some people and voting bots have much lower cost since they don't read, don't evaluate, but only following preset rules.

The main idea is psychic income can exceed the costs, and those who have greater psychic income will vote. Psychic income comes with consuming contents and it may lead more interaction between authors and readers.

In my new post, I suggested other numbers (not zero curation reward!)
https://steemit.com/steem/@clayop/diversifying-curation-reward