There are aspects of the wider fediverse culture that is ignored on lemmy, and thankfully its lack of interoperability has helped it avoid trouble (for now). I'm really not sure how to explain to you how it could be used for harassment as it requires a bit of detailed background to how the wider fediverse functions and its history and I don't really know if it would convince you if I did explain it in enough detail. Just because data is publicly scrape-able doesn't mean it's acceptable to do so.