Comfortable shoes can make a long travel day easier. The useful question is how to stay comfortable and considerate in the actual cabin, rather than treating shoe removal as a universal airline violation.
Choose footwear for the whole journey
Think about walking through terminals, standing in queues and moving with luggage. Shoes that are easy to put on and secure enough for walking can be more practical than footwear chosen only for the time in your seat.
If swelling or a medical condition affects footwear comfort, discuss the issue with a healthcare professional. Removing shoes does not by itself cause swelling, and footwear advice should not be presented as a diagnosis.
Respect shared surfaces
Keep feet off another passenger’s seat, armrest and tray table. Wear shoes when walking through the cabin, especially when visiting a lavatory. Avoid leaving loose footwear where someone may trip over it.
Socks can be a comfort choice while seated, but they do not make placing feet on shared furniture considerate. Strong odors can affect nearby passengers; use the same courtesy you would want in return.
Follow the crew and stay ready
Follow any footwear or movement directions given by the crew. Keep your shoes within reach and avoid creating obstacles around your seat.
There is no single rule requiring every flight attendant to make every passenger keep shoes on throughout every flight. Airline policies, equipment and circumstances differ. Choose comfort without creating a problem for the people sharing the space.