How would the USA be now if President Lincoln had shipped all African slaves back to Africa?

really hard to say - but I believe civil rights would have taken much longer to be enacted, we would have missed out on so many cultural, medical, intelectual enlightenments, would have suffered economic hardships. Racists are gonna be racists, they would have found targets regardless, and you just cannot fix stupid. Diversity is a strength, and also a weakness - a strength because learning different values, norms, and cultures make everyone question and critically analyse their own values and norms usually ending in making both stronger through understanding. - a weakness because when you have so many different values, norms - they tend to cause strife through self interests, making it easier to be exploited and divide. Is slavery a horrific part of our history, absolutely - but it is part of every nations history, and is still alive and well through human trafficking here in the west, actual slavery in Africa and the Middle East, and host of other places. I would like to think we, who have served, have avoided the traps and race baiting that both the liberal left and conservative right have been engaging in recently. I would like to think and believe that, through the hardships of the WoT, looking left and seeing an American and on your right an American, and whether that persons skin color was black, white, brown, yellow, red, or any shade in between, was irrelevant. The important thing was you knew they had your 6, and you had theirs. Nothing makes racial and identity politics insignificant like surviving hardships together.

There were elements in America that tried to do that. I think it is fortunate they didn't succeed.
https://en.wikipedia.org/wiki/American_Colonization_Society

Poorer qualitatively and quantitatively

I'm Not Debating With You SGT (Join to see) I Know When I'm Out of My League. I'm Just Glad to Call You Shipmate.

So you are comparing people with Gender Dysphoria to Slaves? That a stretch. There are one tenth if one tenth of one percent. In the military less then that. The military is not a social experiment. And there different standards for men and women.

Something you may find interesting: https://www.youtube.com/watch?v=qhEvbWD5U1Q

Well, racism still would have been a thing. It may have taken longer and initially focused on different groups, but it would have happened. I agree with Jack Durish that there would have been innumerable losses. Especially to the culture of the US. Could you imagine the US without blues, rock, gospel? Heck, imagine the world without peanut butter. Light bulbs....yup; at least the filament that made them work for longer than 5 minutes - Black inventor. (and as usual Edison got the credit, because he was Edison...and an enormous egoist). The pacemaker, invented by Otis Boykin, the gas mask by Garrett Morgan, mobile refrigeration (don't remember his name now...Google it!), and many others. Where would we be without these things? How many people would be dead today if it weren't for the pacemaker? How many more Soldiers would have died in WW1 without the gas mask? And of course the modern firefighting self contained breathing apparatus was developed at least partially from the gas mask as well. How many lives has THAT saved. I'd say that the US would be so much different now that it would be crazy. And we'd be worse off.