The way I read the OP's post, I got the impression his/her main beef was the lack of consideration that the occupant of 17D was exhibiting to his fellow passengers. It sounded like he made no effort to cover up, blow his nose, not use hand sanitizer, etc. ANC made some very valid points about the economics of changing plans. Those comprise a separate, but related, issue.
If I'm sick and still have to travel, I will load up on Kleenex, hand sanitizer, whatever, to shield fellow pax as much as possible from my germs. It's just basic consideration and it's not that expensive.