The idea that something posted on Hive should be downvoted simply because it had been posted elsewhere seems brain-dead to me. That said, accounts are free to downvote for whatever reason, even a brain-dead one.

And, there was (is?) a long tradition of people reposting content using the #repost tag. There are after all newbies who aren’t going to search for year-old content from someone they’re following, as well as people who originally voted for it who are long gone.