The providers could mess up the summary translations, or the lack of images could make people write their opinions based off their reachings, and people who could read an inaccurate translation would go to the manga section/battledome and write their own misinterpreted posts based on that. Sometimes spoilers are interpreted in a completely different way when scans are out.
But if someone waits until the actual chapter drops, he would be certain about whatever the fuck he's going to talk about outside the spoiler section.