Ahh, this topic... not new but one that always intrigues me
As has been said before it was something along the lines of "failure to organise on your part does not constitute an emergency on mine." Very apt. If I was politely asked I would consider, however if the interloper was already sitting in my seat before i got there and just expecting me to agree to the swap, I would refuse and the FA or CSM would be called if necessary.
Luckily I've rarely been asked to move - I think this is because most of my flights are business rather than leisure routes, and most of these passengers are travelling on their own so no companions to try to sit together with.
I have to say that if I am moved by the cabin crew just to allow people to sit together I would comply with the request and then complain vigorously to the airline. If it was crew rather than the CSM moving me I would request a chat with the CSm also.
If the crew member was phrasing the direction in the form of a request and my "only if I get moved to an equivalent or better seat" line wasn't working, I agree this is the only reasonable way to handle this awkward situation. I don't want to be the ultra-
W P on the flight pulling a "DYKWIA, I fly 300 sectors a week, I ain't moving backwards for anyone!!!!!" that FAs talk about behind the curtain.
I've got a pearler of a story about requesting seat changes.
...
I replied 'sorry, I specifically requested an aisle seat - you can ask the cabin crew if they can find you a free aisle seat somewhere else' (thinking 'maybe if you'd checked in early when I did you would have an aisle seat too?'). Of course, there were none so she begrudgingly took the middle seat.
Oh dear... I maintain a healthy skepticism of sob stories but sometimes they might turn out to be true...
There's a huge difference between a request - "Would you consider swapping seats with xx_"? - as opposed to a direction - "Sir, we need to move you to another seat".
You are obliged to comply with the directions of cabin crew; you are not required to agree to something that is a simply a request for your consideration.
I'd be interested to know if a seat change so groups can sit together has ever taken the form of a direction - "You
will move so Billy and Bobby can sit together, or the captain will call the police" :?: I suspect (hope) most decent airlines will back up the original seat holder here and tell the hopeful swappers to return to their allocated seats quick-smart.