Manners are nothing more than a set of rules for social situations. The function of a lot of these rules has nothing to do with making social situations flow smoothly, and everything to do with demonstrating that you know the rules.
If something that constitutes good manners could equally be expressed as kindness, and being nice to people, then there’s no issue. Once we get into which fork to use first, and how to eat a banana with said fork, the only point is to demonstrate that enough time and money has been thrown at you to turn you into the sort of person who can eat a banana with a fork, and that you are therefore not a commoner.
I’m a commoner, so, sod that stuff!
What troubles me, is that so often, ‘manners’ are full of assumptions about the kind of body you have. I was sat in the dining room at a school my son attended some years ago, and there was a poster about the proper and polite way to hold a cup. You have to do it daintily, by the handle. You must not grip it in your fist. I have an intermittent shake, and nothing sets it off like overloading a few fingers. If I hold a cup daintily, the odds of my daintily spraying everyone with coffee in a sudden hand judder, are pretty good. I consider it better manners to hold the cup in my hand, or in two hands on really bad days, and not oblige anyone else to wear my beverage.
It’s a small example, but it illustrates the point. The more assumptions there are around acceptable manners about what a body can be asked to do, the more people it excludes. The more demanding the manners are, the more people are pushed out, socially embarrassed, made to feel awkward over things they have no control over. For every daft rule about what we’re supposed to do at the dinner table, there will be people whose bodies really can’t work that way.
My personal standards are based on kindness and utility, not any desire to prove my ‘breeding’. On those terms, I can’t think of many things that are ruder and less polite than shaming people for not being able to jump through pointless etiquette hoops.