I can see your point M.
I think that there comes a point in life where you need to accept that some of your lifestyle choices can and will impact upon other poeple. And I dont think that other poeple should suffer because its not PC to say, "hey, you really dont fit in that seat"
An airline would not let you do it, if your butt doesnt fit into one seat, then you need to buy two.
Tough call though, who wants to be THE person that says something