Yeah, I also never considered any negative stuff! Even if they bookmarked privately, I've done the same a few times, so I definitely wouldn't judge. I think you're onto something re: the antis and harassment.

Also... correct me if I'm wrong, but doesn't the 'mark for later' just lump all the stories together? If one bookmarks something, there is the ability to organize by fandom or any other tags and then later search for specific criteria. Someone who has a lot of fic marked for later (maybe several fandoms) may find it more convenient to be able to sort and filter them.

A very good point!