I'm just trying to distinguish between what people say and what people do. Honor is BS. Always has been, and always will be. Just utter nonsense.
I understand that you might struggle to get into the mind-set of someone from 1862, just as people from 2170 will probably struggle to understand why we do half the things we do. However, this doesn't make honour any less of a real motivation for Palmerston's actions. As Glen Melancon explains:
'Honour governed what we today call "linkage" or credibility because loss of honour would affect what Palmerston referred to as Britain's "moral power" to influence the actions of other states by undermining confidence in its ability to follow through on its decisions. These states must not forget, when facing a British frigate, however small, for example, that the "Flag of England must be respected." In an era when policy was guided by the principle that Britain should not interfere in the internal affairs of other states, the ability to influence their behaviour was more important than in a period in which the use of force was the norm. However difficult for the late twentieth century to comprehend, honour as a motive for violence was taken for granted before the First World War. To dismiss it as a "veneer" tells us, sadly, rather more about the moral values of contemporary historians than it does about the motives of those with whom they deal.'
I can't see it. It's not in the US interest to go to war, which is why we backed down IOTL. It also isn't in the US interest to vigorously prosecute the war and bring down hell on themselves when cooler heads can prevail even after a declaration of war.
The Royal Navy didn't achieve 200 years of maritime supremacy by assuming its opponents just wouldn't bother fighting it. Presumably, though, you will concede that there's a perfectly valid reason for Milne to break the blockade and destroy the blockading squadron that doesn't involve him being a secret slavery supporter: that the US navy is a potential threat to the British. Particularly if you believe, as many in the British government seem to have suspected, that the point of the Trent is to allow the Union to duck out of an increasingly hopeless Civil War and take some free territory in Canada as compensation.
Again, what people say and what people do. It was always going to be a war aim. In less than a year, the Emancipation Proclamation is issued, and Lincoln wanted to issue it even before then. And that's far from the first motion toward ending slavery.
But you're basing all this on hindsight and private information, neither of which Palmerston had the benefit of. What Palmerston knows is what he's learnt through official diplomatic channels (that the Union isn't going to act against slavery); through Lincoln's public statements (that the Union isn't going to act against slavery); and Lincoln's public acts, (that generals who proclaim emancipation get overruled and subsequently sacked). If it was so obvious that emancipation was always going to be a war aim, why did the Union try so hard to convince everybody - including Palmerston - that it wasn't?
But at the end of the day, there is no reason why he can't have two agreements. One with the CS for the CS to pitch in the enforce their own laws, and another with the US to allow them the right to stop US ships.
Then if the Confederates back out, they can say that they consider that the CS wasn't independent when the US agreed to that provision, and that the provision therefore applies to them.
No, he can't. If the British government has entered into a bilateral agreement with the Confederate government, they have recognised the Confederate government as a separate legal entity from the Union. They can't subsequently turn around and say 'actually, we've changed our minds, the Confederacy wasn't independent after all': recognition is final. That's why Britain is so cautious about dealing with Mason and Slidell, and why they send very specific instructions to both consuls and naval captains as to what they should and shouldn't be doing when dealing with the Confederates:
'You are on no account to salute the Confederate flag, but should any of their Forts or Ships salute the British Flag, you have my authority to return it, tho' you are to be most Guarded not to encourage or invite in any manner such a proceeding on their part, or even allude to the subject.' (Milne to Grant and Hewitt, 9 September 1861)
Palmerston is focused on Britain's goals, and nobody else's. He's no more concerned whether a Trent war furthers Confederate independence than he was about whether the Crimean war furthered Circassian independence.
Agreeing to send a few frigates to the Slave Coast after the war (to enforce a law that's already on the books) is a small price to pay to avoid those outcomes.
It was a small price for the United States when they signed the Webster-Ashburton treaty as well, yet they still didn't pay it. Even by the 1840s, Palmerston is absolutely 100% clear on how you should deal with minor states like the Confederacy when it comes to abolishing the slave trade:
'With respect to Spain, Portugal, and Brazil, I must say that the engagements entered into by those Powers have been perseveringly, systematically, scandalously, and dishonourably violated. We are told that the conduct of the Government of Portugal has of late undergone alteration. What I said with regard to Portugal applies to its conduct up to 1839 or 1840. The Government tells us that Portugal has of late begun to be awake to a sense of their obligations to act according to the Treaty... But, Sir, if Portugal has so altered her conduct, what is the occasion of that change? Has it been any spontaneous sense of duty which suddenly came upon the Portuguese Government as the result of their own reflection? Not in the least. If the Government of Portugal are now fulfilling the obligations under which they have, for seven-and-twenty years at least, been lying in relation to this country, it is not owing to any honourable feeling on the part of that Government; it is solely owing to the measure of coercion which we proposed to Parliament in the year 1839, and which Parliament, most honourably, I may say, to parties in both Houses, agreed to adopt...
Sir, I say it was that which brought Portugal to her senses; it was that which brought her to a sense, not of the duty which she owed us—of that she was aware before—but to a sense of her inability to resist us when she was in the wrong. She appealed in vain to the Powers of Europe. She had trifled with us for a long course of years, and when she found that we were no longer to be trifled with — when she thought it would not be prudent to brave us any longer, she submitted...The course which we took with regard to Portugal had, as I have shown, a very good effect with regard to Cuba and Brazil; and if the means were applied which we possess to compel Spain and Brazil to conform to and fulfil the obligations which they have contracted with us, the Slave Trade would soon almost cease to exist.'
The idea that Palmerston is going to trust the very people he believes sabotaged his previous efforts to abolish the slave trade (as well as make a giant diplomatic faux pas by inadvertently recognising them, risking further international fallout and provoking domestic dissatisfaction) stretches credibility beyond its limits. Palmerston was foreign secretary for fifteen years: he knew how the system worked, and (if you look into his career) he made it very clear how he liked to do things.
The UK could not let a country like Ethiopia give them the finger for two years when they were at such profound disadvantages trying to assert colonial dominance over a continent. They weren't worried about honor, they were worried about losing control of Africa if Africans realized they could stand up to white men.
What 'colonial dominance over a continent' and 'control of Africa'? The Scramble for Africa isn't for another fifteen years. At the time of the war, the only African colonies Britain has are the Cape and a few scattered posts in West Africa used for attacking the slave trade.
