I think retaliatory downvotes happen either way if you’re in an argument. Same with report abuse, which, if it happens to a high degree, would be the moderator’s responsibility to ban the perpetrator (reports here are not anonymous like they were on Reddit).
Also, if there’s someone with an abusive mind, they can easily use another instance that shows Activity to identify downvoters. The vote is public either way for federation purposes, they’re just hidden from certain instances - at least on the user level, but they’re still there technically.
I would’ve, or rather had at the time of its creation, fully expected it to shut down either way. Because that’s kinda been the trend with most new Mozilla products from before the new CEO anyway.