So according to MSNBC, pointing out false historical statements is "not legitimate".
First, there were no enslaved Africans in the English colonies until 1654. The Africans who arrived in Virginia had been enslaved by either the Spanish or the Portuguese, but upon arrival in Virginia as privateer booty, ceased to be property and were treated as indentured servants with a standard indenture term of seven year, because that was all that existed under English law prevailing at the time.
It was only in 1654 when an Angolan, John Casor, claimed to be the indentured servant of another Angolan, Anthony Johnson, who claimed to the contrary that Casor was his chattel, and sought relief from a Virginia court, which found for Johnson, that chattel slavery was introduced to what became the original United States. (Notice that the institution itself was an import from Africa.)
Second, the claim that American independence was fomented by slaveholders fearful of British abolitionism is a complete historical absurdity: abolitionism in Britain only became politically influential in the early 19th century, and the calls for independence were loudest in Massachusetts, which had been gradually dismantling slavery by applying British case law, and which completely abolished the practice in the period between American independence and the adoption of the Constitution.
And that's just the colonial period...