Just because the British Empire ended slavery doesn't mean they weren't exploiting people for economic gain- they were and continued to do so for nearly another century. The worst abuses in colonial India happened after the abolition of the slave trade. Would Americans let Britian abolish slavery anyway? The slave states revolted against even the idea of abolition in reality, and that wasn't being imposed by an imperial power across the sea. I also find it hard to believe that native Americans would have been treated any better. The US was going to expand westwards regardless. The Louisiana purchase might not have happened, but we would probably have gotten that territory anyway after Napoleons defeat. Losing the revolution wouldn't make us any less likely to exploit the West.
It's a very interesting thought that America might have revolted over the abolition of slavery
if they hadn't gained their independence before it happened. I'm sure that if the states were willing to revolt against Britain because they had a few taxes imposed upon them against their will, that they'd definitely revolt if Britain tried to force them to comply with something that would have such a massive impact on the American (considerably labour based) economy. And even if the northern states were still as (comparatively) progressive as they were at the time in our history, they'd probably side with the south in order to make a stand against British influence. Just think, instead of a nation divided by slavery, it would be a nation united by slavery. I wonder how different America would be today if the union was founded on a basis of oppression, rather than principles of "liberty", and "freedom from oppression".
Likely, you would've seen the more northern states siding with Britain, since a lot of their workforce was immigration-based. The southern states, which relied heavily on slavery, could have revolted, but without support of every state, they'd likely be crushed without foreign intervention.