I don't blame him for Maleficent either but Xehanort reeked of so much 'eviiiil' that it was ridiculous. They should've off all known better, especially Eraqus.
But yeah, Terra definitely doesn't have an ego which makes Eraqus comments about him being obsessed with power strange because we're never shown that nor do they explain where the darkness within him even stemmed from? Was it jealously towards Aqua. Frustration towards Eraqus? It's just really weird. The more I think about this game, the more I dislike it. :/
Frustration and anger seem to be the primary sources. Those are the only times when it manifests.