|Federalist Papers - Wikipedia|
According to Thom Hartmann and truth-out.org it was required in order to ensure Virginia would enter into the United States. (Perhaps you've seen this on Facebook.)
It is hard to find anything at all historically that addresses the claims Hartmann makes.
The Second Amendment has a long and detailed history from the 12th century related to the English long bow and other arms and the use of it by militia to both serve a variety of functions such as policing as well as to control tyrannical kings (see this and this).
There are a number of web sites detailing the history of the drafting of the Second Amendment.
Nothing I can find seems to relate to Hartmann's thesis.
Hartman claims "Patrick Henry was also convinced that the power over the various state militias given the federal government in the new Constitution could be used to strip the slave states of their slave-patrol militias."
However, the full quote in context says "... If they give power to the general government to provide for the general defence, the means must be commensurate to the end. All the means in the possession of the people must be given to the government which is intrusted with the public defence. In this state there are two hundred and thirty-six thousand blacks, and there are many in several other states. But there are few or none in the Northern States; and yet, if the Northern States shall be of opinion that our slaves are numberless, they may call forth every national resource. May Congress not say, that every black man must fight?"
Clearly Henry is concerned that the "north" (an area that did not support slavery generally) will take away the slaves from those who own them for the purpose of a "general defence" of the country. The "north," where the "general government" would reside would see slaves as a "numberless" resource to be called out when defense was required.
Nothing to do with "slave patrol militia."
Hartmann's thinking clearly falls along the lines of "The Real and Racist Origins of the Second Amendment" available at the www.blackagendareport.com. The idea here is that modern "gun culture" is a "... self-justifying mythology that construes the Second Amendment as arming the citizenry as final bulwark of freedom against tyranny, invasion or crime."
However, clearly everyone involved in the framing of the US Constitution was focused on the tyranny of Britain and providing for a self defense in the context of the country being attacked and, hence, not a mythology at all. (A reasonably detailed description of the framing and acceptance of this amendment is provided here as well as other places resolved by Googling "history second amendment.")
Again it seems that a discussion of some general topic, in this case "gun control," has been turned instead into a question of whether or not you agree with "racism." Effectively that if you believe in the Second Amendment you are a racist.
Instead it seems that the Revolutionary War served as a starting point for blacks becoming free from slave owners (see this as an example as well as this from the National Park Service).
Fortunately for those who care about actual facts incredibly detailed records exist of the framing of the US Constitution - documents involved in the decision making process as well as the thinking, e.g., the Federalist Papers, that went into what was proposed for the Constitution and Amendments.
All of which debunk Hartmann's thesis.
Was the issue of slave ownership involved in the drafting and ratification of the US Constitution?
Clearly as described by Patrick Henry's own words. However, you cannot simply take random portions of the framing and ratification process and jumble them into something that they are not: racism. Slavery remained in the US after the Revolutionary War into the 1800's.
However, the notion that "The Second Amendment was Ratified to Preserve Slavery" as well as its thesis are simply false.