Character Analysis
Fremantle may be English, but he's a total Southern fanboy. He even wrote a book, after Gettysburg, arguing that the South could still win the war. He's at Gettysburg on behalf of the British government. He's observing the Confederates and to help the British government determine whether it should throw its weight behind the Confederates or not.
Fremantle is totally carried away by Southern chivalry and aristocracy, though he does seem to retain some awareness that this is all based on slavery. For him, though, it's more important that the manners and culture of the American South seem similar to the manners and culture of England, whereas the North is multi-religious and multicultural in a way that evidently disturbs him.
Here's a sample of this dude's super enthusiasm:
They called themselves Americans. But they were transplanted Englishmen. Look at the names: Lee, Hill, Longstreet, Jackson, Stuart. And Lee was Church of England. Most of them were. All gentlemen. No finer gentlemen in England than Lee. Well, of course, here and there, possibly one exception. Or two. (3.1.28)
In the process of his supposedly dispassionate observational duties, Fremantle gets totally carried away with the romance of the Southern Cause. For example, he admires Lee with the wide-eyed awe of future generations, while missing the flaws that Longstreet manages to spot.
Still, why would a dude like Fremantle be down with a slave-holding government? Although Great Britain had abolished slavery, it was seriously considering supporting the Confederacy, since the South was a huge source of cotton, and Britain was a huge producer of textiles. All that cotton is a big reason for all these European observers to be hanging out in the Confederate ranks.