But what about people who are in different parts of the world and don't inherently understand your meaning? That is terrible behaviour to downvote the notation.

Text is notorious for not conveying context. Sarcasm can easily be seen as serious by some people, why is why we have the /s notation to make it obvious.

People aren't idiots, they come from different backgrounds, locations, languages, and all use English as a common tongue. Have some consideration and stop thinking you are so big and clever.

The best sarcasm is exactly the one where it could be interpreted as written and people misreading it is part of the fun. If you are going to add sarcasm marks to make sure that absolutely everyone gets what you are intending then whats the point of using sarcasm in the first place instead of clearly writing what you mean?