Republic= liberalism and egalitarianism
Empire = order and hierachicalism
Jedi = philosophy of peace and being at one with the force and attempting to interpret the will of the force
Sith = gaining power through bending the force to your will
Light = benevolence & detachment
dark = selfishness & passion
there are varying degrees that these ideals can be mixed together and that is why it is so contentious.
good and evil are relative...
The force doesn't care about any of these trivial things.
This is my personal opinion. I have very little EU knowledge, but I enjoy the fact that these things can be debated both in universe and by those of us who have taken enjoyment from investing in a galaxy far, far away.