Gaspard primarily uses Celene's support of elves- and by this I mean, offering them a minimal shot at education and participation in society, and rumors that she and Briala are lovers- to topple Celene. So the basis of their estimation of her unfitness to rule is primarily racism and classism. Which goes back to their "code" and its foundations- that they exist to preserve the social pecking order.
Around the common folk, they aren't taking orders, they give them. Like ordering the merchant woman you can meet in Denerim to submit sexually or die. What military objective does that serve?
They're always prattling about their honor, so yes, I do think it's legitimate to evaluate them as moral agents.
1. Well, technically Gaspard became disillusioned with her because he didn't think her diplomacy would resolve the mage/templar conflict and felt she was unfit to solving the war. He merely used the elves as a way to weaken her politically.
Don't get me wrong, I don't like Gaspard, but I also don't like Celene, so I can criticize both.
2. It doesn't serve any military objective. I think this ties into the fact that you have to be noble or of noble birth to even qualify to train as a Chevalier. It's like an upgrade of what Sergeant Kylon in Denerim has to deal with. He's given a legion of ba**ards to command. "A decent pay, uniform, no expectations," and such, as well as the expectation of explaining "to their noble fathers that being a guard is actually dangerous." But all he has to worry about is "dicing, the odd bit of drool or yelling at them too loudly and watching go sob tears in their courtesans bosoms while he gets chewed out by their noble fathers."
I think it has less to do with them be chevaliers and them being nobles and expecting things handed to them on a silver platter, and many of them abuse the power they do have knowing they can get away with it because of their position. Such a thing is not limited to Orlais and its Chevaliers. (Vaughn, *cough*)
Now, I'm not defending them. I dislike the Chevaliers for the exact same reasons, but I also dislike most nobles we meet in the games as well.
Honor codes are subjective to people as such things are just bule prints on how to live by their rules. The honor code is negated by the fact to become one you have to kill civilians in the Alienage. Plus the fact the laws have it were one of them could basicly rape anyone they wanted and get away with said deed.
That's the thing. It's in the alienages. Kendals in Kirkwall targeted elves and no one did a thing about it because it was elves. Elves already are seen as lesser to humans by virtue of their ears. In many instances being a servant is the highest they are expected to rise. Iona in Cousland's origin story says she didn't want her daughter Amethyne getting ideas of rising above lady-in-waiting because elves normally couldn't even get that high and she was fortunate that she did.
It's not the chevalier's targeting the alienages that's the problem. It's the entire perception of most countries that elves are lesser than humans, and thus have less rights. It's the widespread racism of humans that's the problem.