I think you need to deal with the fact that some people would like to feel they are engaging with humans rather than machines and then etiquette is a factor.
I do agree though that some folk are content just with the chess while others like me want my cake and eat it i.e. good, competitive chess and courteous social interaction. Chess.com does well to cater for both types!
These days I tend to play more team games than open invites as this tends to more likely satisfy that need. When I do accept open challenges I tend to check out the persons profile (crude I know) and try to guage the type of person I will be up against.
Having said that, I played people of all types and from all over the world and it has been a fantastic experience.
I know this is one of my bug bears but having now played 150 online games, it seems to me there our two extremes of player when it comes to courtesy and we all fall somewhere in-between - poilite and considerate and impolite and inconsiderate. I've encountered both extremes and (for me) enaging with real people playing chess and the mildest of acknowledgements is one of my motivations for playing.
I appreciate for some their English is poor and/or they are more intent to play chess than chat ... but it seems to me as a minimum we should acknowledge our opponent when we begin and thank (and/or congratulate) when we are through (just as one does in real life chess games). Other things like playing at a decent rate also matter.
Folk who don't do these basics may as well play the computer!