Before downvoting, check the community.
If you fail to use the /s tag or specifically call out that your comment is sarcastic, I'm going to treat it as being earnest. I might ask if you're being sarcastic, but I will downvote as though you are being earnest.
The /s tag not only clarifies, but it also confirms that you're being sarcastic. A thing you cannot ordinarily convey via written text unless you specifically call it out. You can hint at it, readers can infer it, but you cannot convey it. To convey it, sans directly stating it, you would need to include a recording of you speaking the comment, which defeats the whole point of text chats.
"It definitely reads as sarcasm, you're just missing it" So what? I'm neurodivergent. I barely get this shit in its normal, spoken context. Why should I be expected to understand the implied sarcasm in your text comment?
"Telling someone you're being sarcastic ruins it" Unless your definition of sarcasm is just lying to someone's face, you do indicate sarcasm when speaking. Via the exaggerated, deadpan tone you use. Something you can't convey in written text unless you specifically call it out.
"I made it very clear via hyperbole that it was sarcasm" Have you talked to people? Your obvious, over-the-top, hyperbolic sarcasm could just be someone's opinion taken whole cloth. In fact, you probably modeled your exaggeration AFTER a person. Can you see why, if I don't know you, there's no way to tell?
"I forgot the tag" cool, if I see the edit adding it back in, I'll revert my downvote. Consider it the opportunity cost of forgetting.
"It doesn't hurt anyone" Yes, it does. You give credence to your exaggerated position that you would never take because the people who think like that exaggerated position will point to your comment as proof that they have support. It's why 4chan rebirthed nazism.
"I still won't do it". Then have fun with the downvote. You want to make the internet worse? I'll be sure that you don't get the internet points your brain craves.
As someone who doesn't use the /s and regularly gets downvoted as a result, I'm less interested in your downvote and more interested in why anyone upvotes.
For example, if we're discussing American healthcare and you're arguing for universal healthcare because it makes sense, I'm likely to respond sarcastically with "But that's socialism! In America, we'd rather pay and arm and a leg to die from preventable diseases than just secure healthcare! That's true patriotism!"
Now, if you were to take that at face value, I'm curious as to who you think would genuinely argue for excessive payments to die from preventable diseases so blatantly. Literally no one does that. That's not giving credence to an exaggerated position because it's not an actual position anybody would take. But your reaction is beside the point, because I'm not interested in you.
I'm interested in the people who agree with my sarcastic position, often by tamping down the hyperbole, because they're unreasonable. These are people I'm trying to catch with my vinegar honey pot. It might giving credence to their views long enough for them to respond positively to me, but after that...it's all mudslinging. And if someone says they oppose universal healthcare because it's socialist, well then I get to have being extremely sarcastic with them while you get downvote me.
...but in his mind his political opponents aren't people with different points of view. They're stupid people who hold the exaggerated position you laid out without a hint of irony.