I would also add that, to those of us who notice such things, the [person in uniform] who took my seat, if I were the paid passenger in F, is affecting my view of their employer. Against policy or not, that's something AA could care about.

Like others have said, I will almost always do a kind thing to help someone who asks first, even if it inconveniences me a little. (I have mobility issues myself, but not bad enough to require an assistive device at all times, just sometimes. Maybe 10% of my life? But I always travel with my cane because flying is so fraught.)

I also react much more negatively after something I expect (an assigned seat) has been taken away from me unexpectedly.