I personally found the 5th reply to the same comment thread a little repetitive. Unless there is anything more to add to the conversation a simple upvote/downvote on an already existing thread is probably enough. I don’t think I ever downvoted a post though, just because I sorted by top/hot.

These requests are probably made by search/indexing bots. My personal server gets a quite a lot of these, but they rarely use any bandwidth.
The easiest choice (probably disliked by more savvy users) is to just enable cloudflare on your server. It won’t block the requests, but will stop anything malicious.
With how advanced modern scraping techniques are there is so much you can do. I am not an expert, so take what I say with a grain of salt.