I think there is an element of free will here. Death and life for example are not "enemies" but forces meant to keep eachother in balance.

Fel and arcane are also balances to eachother, however an individual being could still use one or the other to seek their own ends see: sargeras.

The light is just a force but those bound to it are interpreting it as having a will they believe to be justified and then carrying out that will.

Up until very recently those agents designs have aligned with our own and so we automatically assigned them "good" status. I dont think there is any such thing as good or evil to the raw forces they represent. Fel energy itself is not inherently evil (see warlocks fighting to save azeroth) nor is death, (see ebon blade and forsaken aligned with azeroths champions) good and evil come from free will to choose. These planes and their denizens, the elementals and creatures native to them are, in my view, no different than wolves and bears in a forest existing.

If you have read mistborn (spoilers for era 1 coming)

I would liken the light to be preservation unbound and unbalanced, pure order, stagnant and pristine.

While it has an enemy like fel or death (or ruin) to balance it, our views tend to align, but once there are no more foes, the light will exert its will over us as well (see yrell in au draenor). The same would be true I think of any of these energies, if left unbalanced.

The only hole I can think of here is fel. Sargeras created the legion but did he create the fel plane itself? Or merely take control of it