The following reflects just the views of one of the mods. Many posters, including some of the moderators, successfully include sarcasm among their rhetorical devices, without running close to the boundary. I just checked the TD Comment Policy and, as it happens, sarcasm is not even mentioned by name. But, as you note, it is a sharp-edged tool. That means it requires some care. Some people have the talent to use it well, and some just don't seem to, despite repeated practice. And when it falls flat (always a subjective matter), it will come across as simply being combative or a setting up of a straw-man. Rather than try to give ever-more-detailed guidelines on how others use sarcasm well, I suggest going back to the simpler statements found in the Comment Policy: Respect for others is expected in everything we write, and personal attacks are not allowed. and TD encourages humor, but please consider how someone who doesn’t know you might interpret your post. If you can use sarcasm while heeding this, to try to dismiss an idea while not dismissing an individual, go for it. Watch this video of comedian Keith Alberstadt: [video=youtube;I-SFA5Xs0s8]
Decide for yourself which of his jokes would translate well to the written medium even when the live performance aspects were missing, and which ones he would perhaps "call an audible on" if posting here.