They damage the motivation of scanlators and enjoyment of readers all for a tiny ego boost leeched off of some barely scraped together ability to understand primary school Japanese. The world would be a better place if they simply stopped posting entirely. Forever.
Uh you're pretty harsh there. I don't think most people posting spoilers are looking for kudos for their ego, but are usually just excited and want to discuss it with others.
I personally don't mind small spoilers that are hidden once in a while, but it does look bad when it's like pages and pages of black bars or when it's paragraphs of summary. I think a good rule is to just stop when people tell you to stop.
I think this is where a dm system would be nice for those that do want spoilers, but I guess there's discord and whatnot for that.