Tom you witnessed something that happens on many cruise ships and on land. I am fortunate that my wife is not in a chair yet, but will be at some point, however my wife is handicapped and gets around with a full length leg brace. We have seen the rudeness of people not only on the elevators but finding a seat in the shows or even trying to get onboard or into the dining room. I have even seen people try to take the seat right out from under my wife when she goes to release her leg brace to sit down, which also happened to be on the Mercury.
On one cruise a lady actually grabbed my wife and yanked her backwards, almost causing her to fall, to try and get on the elevator first. This lady found out I do not tolerate that and I removed her from the elevator and let my wife enter. She and her husband did not argue with me because I am a little intimidating in size and looks LOL.
Unfortunately there are some people that still believe they are more important than everyone else and that they have the right to be first. I am glad this is not the majority but their behavior does stand out.
I was raised in a family that had people severly handicapped due to polio so in my case I learned at a young age to be patient and tolerant of rude people, however it is frustrating to see how people ignore the handicapped.