Earlier quoted context omitted.
Just as a great comedian doesn't laugh at their own joke, great sarcasm is best served without a sarcasm tag.
I disagree when the medium is text; it's harder without tone to hear.
But does that mean one should always put in a tag? It may ruin the joke.
As an example, this was one (or two) of my highest-voted HN comments ever:
https://news.ycombinator.com/item?id=8690893
If I'd added a '/s' tag to those comments, it would have spoiled it, wouldn't it? Part of what made it funny was that I played it straight, and people believed I was sincere almost to the end - or beyond.
But now I fear I have led us far off topic. Back to our regularly scheduled discussion of Facebook, watchful defender of our privacy.