Freedom of speech is a law regulating actions the government can take against you for saying what you want.
This is a discussion about etiquette, in other words how we behave toward eatchother in a society.
If you start referring to freedom of speech laws in normal conversation you have already breached the rules of etiquette, while at the same time displayed your ignorance of how freedom of speech works.
In this case the etiquette invites the person to shut the fuck up after being told no in a polite manner, while the law allows the person to bitch about it. Then we have to consider the rules of the airline, what do they say about swapping places?
Personally I would have no issues changing seats given three conditions:
- The new seat is equal in comfort to my old seat, I am a fat guy (dealing with it) and I will not sit next to another fat guy.
- There is space in the overhead locker for my bag.
- I have not paid extra for my seat, if I had I'd expect some compensation for giving up the added value I paid for.