Lincoln may have disagreed with his client, but argued for him in court, certainly.
But someone who is morally opposed to slavery would likely feel serious qualms about taking money to keep people enslaved.
But not about talking money to keep a murderer out of jail.
Unless they are the FedGove relying on Import tarriffs paid by Cotton sales. Then taking money to keep people enslaved is just fine.
As a matter of fact, had the Fed Gov announced it would no longer take any money derived from Slavery, it would have had a moral case against fighting against it.
They did not do that. No, it appears they were simply fighting to make sure they kept getting their share.