There was some debate about the rearward facing seats some years ago and although it was proven that rearward facing seats are indeed more safe, passenger would never adapt to it. I know I personally never like to sit rear facing on a train for example.
Working for BA I do get a fair few comments from passengers in Club who suddenly get onboard and realise that they are sitting backwards. Many do not like the sensation of taking off backwards and I suppose to those who are sufferers of motion sickness it can be stressful to them.
Also, and heaven forbid it should happen, I could easily see passengers adopting the incorrect brace position when sitting rearwards simply out of habit of seeing the conventional brace position from forward facing seats. In Club those facing backwards are asked to remain fully back in their seats with their arms crossed over their chest.