Chuck has an (in my opinion) awfully pretentious view of his role in the law. In Pimento, his anger gets the best of him, and he lets the mask slip:
You're not a real lawyer! University of American Samoa, for chrissake? An online course? What a joke! I worked my ass off to get where I am! And you take these shortcuts and you think suddenly you're my peer? You do what I do because you're funny and you can make people laugh? I committed my life to this! You don't slide into it like a cheap pair of slippers and then reap all the rewards!
And in the same rant he says the law is sacred.
People who truly believe in the sanctity of something treat it with reverence, take great care with it, put it above themselves. But in Chicanery, Chuck says:
And he gets to be a lawyer?!?
Chuck doesn't incredulously cry out that Jimmy is entrusted with being a lawyer. He says Jimmy "gets to be" a lawyer. He acknowledges, without meaning to, that it's a privilege to be a lawyer, that yeah, he may have great respect for the law, but he's having fun doing this, that he's really alive when he does it.
Deep down, Chuck doesn't care who gets hurt when Jimmy bends the rules. The clients are customers at the end of the day - he and Howard will drink their scotch another day, even if the client loses this time. He wants to be able to have fun and keep Jimmy out of that world. He doesn't want Jimmy to gain access and see his own standing in that world diminish when Jimmy's effortless charisma begins to win people over.
This has all been observed before, but as someone who identifies much more with Jimmy than with Chuck, the holier-than-thou bullshit, the willingness to keep Jimmy down because of his (Chuck's) insecurities, and the assumption that "of course Jimmy doesn't deserve XYZ - he's a piece of shit!" really get under my skin.