There is a comfort factor that is violated when a familiar system is junked in favor of a "new and improved" system. Some folks just resist changing. The new discipline system will hopefully have a good impact overall, but fear of the unknown and the uncomfortable adjustment to a new system will lose some folks. Just simple psychology.
As for myself I trust the designers to have the big picture more in view. According to what I read EA is losing money on SWTOR, this might turn that around. A little faith that they want us to enjoy the game more too should offset the fear of the changes. I think the only constant in the Universe that's always guaranteed is it's always changing. Let's support the idea and see what happens.