What irony and hypocrisy. You conveniently gloss right over the direct role Great Britain played in establishing slavery in the Americans to begin with, for Britain's ongoing slave trade for the first two centuries after its American colonies were founded, and for the enormous slavery-based profits shipped back to Great Britain from the Americas. Yes, it's a shame that slavery was dumped upon the American colonies by Great Britain to begin with, leaving the newly independent US to deal with what was by then over two centuries of established slavery in those former English colonies, and to eventually have to fight a Civil War to rid itself of Great Britain's "gift". Civil Wars and 600,000+ dead do tend to leave hard feelings for generations, and at the time of the World Wars there were still Americans living who personally remembered or actually took part in the Civil War, or were no more than one generation removed from it. Btw, the slaves didn't free themselves. The vast majority of abolitionists and those who fought and died to finally end slavery in the US were some of those same white Americans you tar with such a broad, cartoonish brush.
It also didn't help matters that Great Britain's enormous appetite for Southern cotton and other plantation-produced goods continued to help support Southern slavery and keep it profitable for the 80 odd years between the American revolution and the Civil War. In the meantime, Great Britain could posture, preen, and claim the moral high ground by not having slavery in its homeland, while at the same time encouraging, supporting, and profiting from slavery overseas.
So much for smug moral superiority.

black people didnt have any stature in 1939 in Europe
Yes they did. There were black lawyers, doctors, Royal Navy captains etc. in Britain before your Civil War! The way white Americans treated black Americans, during their stay in Britain, during WWII, caused a lot of animosity.
"Those Americans are so polite, modest and respectful. It's a shame about the white blokes they've brought with them!" was a common quip.
England, is devoid of racial consciousness [the English] know nothing at all about the conventions and habits of polite society that have developed in the US in order to preserve a segregation in social activity Butcher. (Aide to Eisenhower).
The white Americans were afraid that the black Americans, having been accepted as equals, might get 'uppity' when they returned home. I'd love to think they were right!

He was a composite character.
Agreed, he played a fictional character. Dramatic license notwithstanding, in this case I don't quite see the point of making him such a central, headlining character to proceedings.

He was a composite character. But the movie shows he wasn't a celebrity just respected by some in the north

He was the uncle Tom

It wasn't like Freeman/Joadson was depicted as some kind of celebrity or something.
Some free blacks in the North were able to gain prominence, although they certainly faced very serious racism.

4. You ever seen Superman $#$# his pants? Case closed.