Just commit, no matter the response. Adding /s is akin to explaining a joke after you tell it. If someone doesn’t understand or pick up on the sarcasm, it’s not your responsibility to spell it out for them. You add /s because you don’t want to be held accountable.
You’ve ignored the wider picture with this. There are generally 4 categories in which all comments fall:
If everyone used /s 2. and 3. would disappear. Yes, you can think it is cowardly to avoid 2., but I think it is much more important to also avoid 3. by tagging all sarcasm.