Subconscious bias may or may not take place in a specific case. Interviewer's bias can be with regards to race, sex, hair color, nationality, accent, physical fitness and so on. We may keep arguing about which if them plays higher role in me being hired.
HR policies, on the other hand, is an objective reality with a measurable outcome.
In a specific case, certainly. In the general case, subconscious bias plays a role.
It doesn’t seem like a real argument that, generally speaking it is unknown whether race or gender bias is more of a determinant in hiring decisions than hair color bias. Is that an argument you consider rational?
HR policies do have measurable outcomes. It's a question of what you think those measurements describe. A diversity hiring HR policy is a counter-action to the existing subconscious bias favoring white men, and a long term effort to squelch subconscious bias favoring white men by increasing exposure to diverse races/genders. Let's collect some long term data and analyze the result measurements, instead of pretending subconscious bias favoring white men doesn't exist.
HR policies, on the other hand, is an objective reality with a measurable outcome.