Two peeves in one here:

The "/s" is just punctuation, same as "!" or "?" or even ".", which was a radical suggestion at one point. Punctuation isn't bad, it's not necessarily good either, but it is often useful. It should be judged based on whether it improves the ability to communicate via the written word by encoding nuance that would have been expressed verbally.

And A Modest Proposal isn't comedy, it's also not sarcasm, it's satire. Modern satirists may have confused themselves into thinking that the point of satire is to be subtle, but this is a disastrous idea. Satire is political commentary, it's supposed to be so over-the-top and starkly obvious in its intent that it cannot possibly be misconstrued as accidentally arguing in favor of what it's trying to argue against. This is why, for example, Paul Verhoeven's Starship Troopers is bad satire: if someone has to ask "is this satire?", or someone has to helpfully point out that something is intended to be satire, then it's bad satire by definition.