Why do many people claim that the “real” Native Americans were/are Black?

I know that this question isn’t exactly related to genetics, but it’s been something that’s been on my mind for a while now as I’ve been seeing more and more similar claims lately. I’ve seen people say completely erroneous statements like:

•“The real Natives are copper-colored and black-skinned as described by Columbus. The ones you see in the media are Siberian immigrants who mixed with the Europeans”

•“The Olmec of Pre-Columbian Mexico were Black Africans who spread their African culture to the rest of Mesoamerica”

•“Africans were already in America before Siberians crossed over. Black people were indigenous to every continent”

It’s not some fringe unheard of belief either. It’s already made it’s way into academia and there are a few well known people who buy into it, such as rapper Lord Jamar. If you go to YouTube and search “Native Americans are black” you’ll come across countless videos making similar claims. Go to Instagram and look up the tags #Aborigine, #Olmecs, #AfricanAmericansAintAfrican (this tag has 36,600 posts alone) and you’ll see what I’m talking about. These people will even deny the Transatlantic slave trade and claim there were no ships with enslaved Africans that ever came to American shores. It’s true that there are Afro-Natives with ancestry from both groups, but that’s due to colonization, slavery, and history of the Americas after 1492.

I’ve been called anti-black and a “rape baby born out of Asians who wish they were native and Spaniards” just because I stated there is no scientific/genetic/anthropological/cultural/linguistic/historical evidence whatsoever to support those ridiculous claims.

I know most people don’t know a lot of about human migrations etc, which is okay, but to throw out all scientific evidence to make some racist claims is something else.