I believe it's not just a badge; it's a layer of protection against scammers. When you see a seller with hundreds-or-more feedbacks and none of them negative, what does that tell you? That they've done everything perfectly and never had a problematic buyer? -That's almost impossible. More likely they have dealt with problematic buyers by doing whatever it took to avoid negs, and they'll likely keep doing it, just to keep that pristine 100%. Put yourself behind a scammer's eyes, and that's a nice target.
Another thing, some buyers carry the myth that some sellers are able to get all their negs removed no matter what the details. So if you put yourself behind the eyes of one of those buyers, a 100% pos may not be the badge of trustworthy excellence the seller thinks it is. That buyer could view it with suspicion that the seller just gets away with it when they treat buyers badly, so another seller offering the same item but who is obviously not immune to consequences (because they have less than 100%) is a better option. -And I'm not just speculating on this; I've seen numerous buyer comments about not trusting 100's.
And finally, no buyers are such idiots they can't tell meaningful from meaningless feedback. They can read negative comments and tell if those buyers had unreasonable expectations and/or blamed the seller for things out of their control. So the only way those can really hurt you is if you have enough of them to drop your score so low that buyers just scroll past your listings without reading the negative comments.
I just checked and apparently my 1 neg is going to roll off in June or maybe July (June 18th sale but it was International so the feedback was considerably later). If I'm even the slightest bit looking forward to it, it's only because I would change my reply a little bit, but getting that 100% is not something I really look forward to.
