Dabble.com founder and "veteran Silicon Valley technologist" Mary Hodder offers the most rational explanation I've heard to date for what happened with regard to gay and lesbian book sales de-rankings on Amazon, in a post at TechCrunch. She expands on a report that a French employee was behind the "ham-fisted," as Amazon called it, mistake:
This of course doesn’t explain how the problem arose two months ago, and why when Amazon was notified, they didn’t look into it then. I would suggest that the same underlying assumptions that drove their classification and algorithm system to be built to filter “gay” into “adult” also led their investigations in February and March to lead to nothing. It was only public outrage this past weekend that caused them to look harder, beyond their own assumptions, to find the underlying problem.
I would suspect that subconscious discriminatory assumptions are built into plenty of algorithms as similarly as they're built into the human mind.
Why Amazon Didn't Just Have a Glitch [techcrunch]