Its public transport and if you don't like mixing with the general public fly in your own private jet!!!!!!!
Why should they have to?
If I had paid good money for my own private seat, I don't expect other people to take up some of the space that I have rented for the duration of the flight.
So do smelly people, rude people, people who have loud clothing and I could go on and on.
Yes, you could go on and on (and you probably will), but rude people and people with loud clothing are easy to ignore and have little or no affect on my comfort whilst flying.
Smelly people are a bit different and can cause problems, but in general they don't worry me or have too much of an influence on my flight comfort.