NOTE: I didn't downvote you. I almost never downvote people, and here on HN specifically I don't have enough karma anyways

I wish there was a way to both downvote and anonymously provide feedback.

With the thread of retribution downvotes I can understand not wanting to both downvote and publicly say you did so, but it would be nice to have a way of saying what it is you objected to.

I also wonder if websites could then use that data to fight astroturfing (e.g., if an account consistently downvotes without providing feedback does that indicate a higher likelihood that the account is being used to influence the site without trying to contribute to and improve it?, etc)

Totally agree. I just wanted to say thank you.