Raiden is a pure being.
He is so pure, that he is capable of entering the Jinsei and exchange energies with Earthrrealm's life force.
As always, he seeks protection by the means of justice. Raiden has tolerated eons of Elder Gods omission (notice that they did NOTHING on this game, they were waiting Shinnok reach the heavens after killing everybody), protecting Earthrrealm alone and dealing alone with people like Shao Kahn.
What happened is the same when Onaga's presence corrupted his being. The infected Jinsei awakens on him a machiavellic mind, he just looses all those principles that keep him from doing all he will do now. Raiden is now even a challenge to the Elder Gods' will.
He came too close to Shinnok's soul. And now, he let himself corrupted by the Amulet.
He is not evil, he is cruel, machiavellic and he is tired of Elder Gods' omission. Now he makes Earthrrealm's rules.
We know where that will lead...poor Raiden. Always trying to save us, taking the ultimate sacrifice, and always getting tired. Without condemnimg or condoning, I understand him (no Manhattan jokes), but he will doom us all the same way - or even worse - he did before.
That's why he is awesome. Too human.
Sent from Earthrealm