I'll always try and help if it is a polite request, but what always makes me livid (and very stubborn about moving) is if I board...and find someone already sitting in my seat! Then they say something like 'I didn't think you'd mind...'. Never happened to me in F, but it has happened to me on several occasions in Club Europe and once in Club World.
Last time someone wanted me to swap from 64A to 63A which definitely wasn't acceptable.
Preferably I think people should wait til everyone's boarded before asking - there may be some unexpected empty seats which could resove the issue without having to disturb anyone. Especially on BA departing LHR when half the transfer passengers have missed their connection due to delays...
The other thing that always strikes me is how such requests nearly ALWAYS seems to involve moving to a worse seat! Very rarely to a better seat...
I mainly travel on my own so I think maybe I am especially vulnerable to being asked.
I think most people may be more open to moving if the request comes from the Cabin Crew rather than pax...

And I personally WOULD be happy to move from row 1 to 2 if asked nicely (assuming they hadn't just sat in 'my' seat!)....the only seat I wouldn't move to would be one of those middle seats...!