You are not taking into account that not everyone lives in the same timezone, not everyone can watch the episode at the same time, etc. Usually there is a "grace period", it varies from site to site, as well as depending on the type of media (e.g. people were tagging Han Solo's death as a spoiler as late as 4 months after the release of The Force Awakens, although that was probably an exception), but for TV shows it's generally something like 48 hours, and this is more or less how we've been doing it here on KYM for as long as I remember – waiting a few days after the episode airs until removing spoilers. There is another debate, about what counts as a spoiler in the first place, because there are small details that don't reveal anything important, and we had a bit of a war with the mods back in May about what counts and what doesn't. So if you are not flagging something as a spoiler because you don't think it spoils anything, that's one thing, but if you're not flagging it as a spoiler simply because "it's already officially released", don't be a dick towards those who haven't got a chance to catch up with the episode yet.