He never lies to you? Really? That's a bit rich considering that he comes to you in a disguise that was deliberately made to fool you. That is pretty much the definition of a lie. He also lies about Stelmane and he does threaten you if you treat him badly. Sure, he protects you with Orpheus' powers but that is only because he needs you i.e. someone outside of the artifact to work towards his plans of liberation from the Elder Brain.
Think about it from his perspective. If he shows up as a mind flayer, there's zero chance for you to trust him. He withholds information out of necessity.
What's the lie about Stelmane?
So, does he have good intentions? Not really. His intentions are only as good as his nature - which, as a soulless parasitic braineater, is still pretty bad all things considered. Acting out of self-preservation might be neutral when viewed in a vacuum, but given the context of what he's preserving i.e. the existence of a mindflayer that eats human brains and enthralls people, it doesn't seem so neutral after all (which is what Ansur recognised as well).
His intentions are good considering what he intends is to stop a threat to all of Faerun. That thing is also a threat to him, yes, but his actions result in an outcome that is good for everyone. There are a lot of things that feed on people. We have no evidence that what he says about only eating criminals is a lie. I've probably got a bigger body count than he does.
People say "oh, but he doesn't choose to betray you and dominate the brain instead of destroying it" like that somehow means he's a good guy. What it really just means is that he's not bad enough to seek out total world domination (low bar) or maybe he suspects that if he went down that route, enough powerful factions would eventually come after him to guarantee his demise. Maybe he knows that if the three chosen of the Dead Three failed, he would also eventually lose control over the brain which after all is the one who possesses all the power of the Crown. Anyway, the absence of total evil is not proof of good character.
It's actually a pretty high bar when world domination is right at his fingertips. There isn't really a better test of one's character than giving them power and seeing what they do with it.
What's far more interesting is that when faced with an actual moral dilemma in the case of Orpheus, he never even tries to hedge his bets by entertaining the possibility that Orpheus might help out and instead opts for the nuclear approach of siding with the brain if you don't want to doom the Gith for his paranoia. He has the choice between the possibility of death or guaranteed subjugation and he instantly chooses the latter. Now, of course he doesn't have player knowledge and the whole scene is mostly a plot contrivance anyways but it still tells us enough about the character to not feel even a little bit bad about siding against him.
I don't think his refusal to work with Orpheus is unreasonable. Orpheus can see we haven't turned illithid yet. It's entirely possible he'd be less amicable if the Emperor was standing right there. I think him having access to world domination and relinquishing it is a better indicator of his character.
