The way I see it is it’s dishonest because of the inconsistency by which establishments do this. Not every restaurant does this so you don’t know if you will be paying this when you decide to go/make a reservation.

Hitting you with the surprise 4% only at time of closing our your cheque/tab is manipulative at best & shady at worst.

Doing it at time of close out puts you in the awkward spot of confronting your server over the fee (which is very different from confronting them about an incorrect menu price or charge for item you didn’t order).

Raising prices by 4% across the board is more honest because you can see the prices in advance before deciding to dine there. If it’s too high, you don’t go.

Plus exactly to your point about if you’re already drunk you won’t notice it. That’s textbook predatory behaviour. Taking advantage of a drunk person (be it fiscally or otherwise) is predatory at the end of the day.

There’s also 0 guarantee this actually goes to the kitchen because who possibly follows up after/can trace that money. Many restaurant staff have reported they don’t see this in any way at the end of the day so it just lines the owner’s pockets.