Every time I read yaoi... little things like this are brushed off saying that this is just "entertainment" or don't focus on it too much....but you my friend have observed and told the truth and for that I really compliment your honesty ...world needs more media literate people like you
it's less hypocritical than that. in-ah knows the rumors of what the crown prince has been doing. if it were someone less malicious, he might be considerably less upset, but with the prince's cruelty and regarding of people as disposable, in-ah's reaction is more like someone finding out their loved one is being hunted by a ravenous beast.
Our ML In-ah is suspicious and angry at the crown prince for his vulgar and filthy eyes toward his brother-in-law when, from the start of this story, he himself has fantasized and even spent nights polishing the wood thinking about the same brother-in-law!
(with this I'm not saying that the crown prince is not a piece of garbage for the abuse towards his servants but that the ML shouldn't condemn him for impure thoughts when he's doing the same!)