With the enormity of our community it's really hard to judge by mere text if what we read online is serious or not. Since all of us here do not know each other personally, we do not have context on what the poster's disposition or their character is. Thus we cannot judge the text based on that. And of course what others might consider as unrealistic might be normal to other people's point of view. So I think it's okay to be on the side of caution and add /s just in case.

Happened to me too and it always disappoints me a little, but I figure if someone doesn't get something that is just blatant sarcasm, that's not on me.

I got banned from reddit because I declined to clarify whether something was sarcasm, because it was just too damned obvious.