[nollidge]

The problem is that sarcasm or ironic speech is meant to subvert the listener's expectations. You say something, people initially hear it straight, but then realize it's ridiculous and you're not being serious, and they find the juxtaposition amusing.

If you demarcate such language beforehand with backtalics or <sarcasm> tags, then there is no such juxtaposition and thus no realization.

Plus, while difficult, there are ways to hint an intonation in text.

I mean, hel-LO, it's so OBvious.

[scott_s]

Most people use their tone of voice to indicate sarcasm. When someone uses a sarcastic tone of voice, I submit that we don't initially hear it straight, back up and rethink it.

Your thinking only applies to a true deadpan comment with a straight tone of voice - that's not the majority of sarcastic comments we hear.

[ax0n]

Indeed. It's like having to point out irony. The subtlety of well-played irony and sarcasm are part of what makes them so great.

[lesterbuck]

Backtalics seems to be a neologism. I kind of like it.