Just to be clear in case this gets heated, I see this as an interesting debate, and nothing I say is intended to offend. I follow your posts because you are generally insightful and interesting even when I disagree. So few people are :-)
The difference is that the 4th was not put in place entirely to protect slaveowners, but the 2nd was. ...
It's false "whether or not it existed"? If the motive existed, then how could it be false?
Primarily because of your insistence on the world "entirely". All it takes is one instance of a single countervailing motive to disprove, whereas you would need to disprove every single alleged instance of any other motive. I am not disputing that slave-owners existed, that they were political, or that they tried to protect their perceived interests--- nor that racism exists today. That much is self-evident from any appraisal of history. I strongly debate your idea that this was the primary or sole influence and your insistence on ignoring the pre-existence of the right in jurisprudence or the radical changes in the views towards slavery as an institution post-ratification and, specifically, post-Eli Whitney and the sweeping economic changes brought by the cotton gin. It would be your burden to disprove all of that, even stipulating evidence that ulterior motives were present and that the ratification debates are quite important to the question. It is that specific burden which I have yet to see any of the RTKBA-slave-patrols proponents attempt to tackle.
Another slice of it is this: you have a home owner who is surprised by an armed intruder in the middle of the night in their bedroom hallway. The homeowner kills the intruder. Would it be valid to claim that the killing was motivated solely by anger? Even given evidence that the homeowner was angry at the intrusion? Who would not be at some level, even if fear was foremost? Other motives are clearly also present and, absent evidence that their actions were unreasonable on their face, those factors are probably of greater legal relevance. It would be the burden of the State in that case to prove that nothing else substantially motivated the homeowner besides anger or personal gain or whatever (that no reasonable person would have been in fear for their life, as in the OK Pharmacy Shooting where a white business owner was convicted of Murder I for shooting ("executing" is probably not too strong a word) a black teen assailant in a Castle-Doctrine state). Do you assume that someone who rescues a victim from drowning was entirely motivated by the desire to be a hero and that no charitable motive exists or does that contention require great proof?
In the same way, I see no reason to suppose that enshrining a pre-existing right already in the British BOR, in the common law the Colonists inherited, in literature that the founders commonly referred to, and already recognized at other levels in these United States, is unreasonable on its face, therefore it is simply unnecessary to presume that ulterior motives had any dominating effect. Burden of proof would therefore be on the accuser that the purpose of the 2nd was to protect slave-owners, particularly, e.g. Pennsylvania slave-owners who would hardly have been a strong political faction. I see no reason to even assume that that slave patrols were Mason's sole motivation given evidence that he possessed other motivations. The admitted vileness of other motives really doesn't factor in: it's interesting for academic debate, but it doesn't really matter to any substantive policy question unless you are arguing that the RTKBA should be interpreted in a racist manner as only applying to whites.
Does the 4th also protect tax evaders, pirates, and smugglers (who were definitely a strong constituency at the time)? Does it also protect insurgents? Might people support limits on law enforcement because they intend harm? Sure. But why do you impute that this was a primary purpose of the 2nd but not of the 4th? How about the prohibition on cruel and unusual punishment which arguably only protects criminals?
Are you saying for over 200 years people didn't understand the Bill of Rights until Edwin Meese explained it to us?
The Peruta court found no problem whatsoever picking out a consistent history of pro-personal-defense case law and debate throughout US history. It is also the case that there have been counter-movements throughout our history, especially in urban vs. rural culture. In the same way, the RTKBA is recognized in English case law going back to (at least) the late 1300s. That does not mean that various British regimes did not attempt to restrict it nor that popular views did not ebb and flow over that time. British case law further connected the right to Dane Law precedent ("restore our traditional rights") and frequently quoted Aristotle and Cicero in that context (e.g. the origins of Castle Doctrine which are still cited today). It was also determined in that case law that it made no never-mind the fact common arms had progressed from daggers to bows to crossbows to handgonnes over that span of time, that the right still applied.
In the US, the Supreme Court consistently neglected to hear any substantive case on the issue for over a century, thus leading to a gradually widening split in the state interpretations of the 2nd. But why e.g., did Missouri, in its pre-and-post-Civil War Constitution, very specifically protect the RTKBA and renew that protection in the 20th century if the popular view did not exist? How do you explain New Hampshire or Nevada or Arizona or the fact that the common law Armed To the Fear of the People (GATOP) offense has been consistently restricted in case law and statute from the 1800s to the present? Again, claiming that the popular or legal view did not exist assumes a high burden of proof that my position simply does not require. If I can produce even a single counter-example, your case fails.
If you took the position merely that the founders were human and had a mix of motives, some of them not very charitable, as you did state at one point, I have no reason to dispute that, nor in fact did the founders themselves. I believe the founders accomplished significant things, but I am in no way pre-disposed to founder worship. They did many things wrong along the way, just as we have in our turn. I think it is also clear that their "innovation" was primarily lower-case "c" conservative, that they looked back to tradition and precedent while at the same time trying to account for inherent limitations of humanity and make traditional structures work better. The whole debate about lower-case "r" republicanism is laced with that philosophy and so, really, was the debate about the role of arms and militia/military structures. A feeling of "legitimacy" (real or imagined) to their structures was clearly important to them and therefore they went to (what they viewed as) traditional forms as their first preference. The British BOR and existing common law was one of those traditional forms (viewed through the lens of their day and the self-selected nature of the Colonial populace).
And yes, I do like Maier (and not particularly Levin), as she shows less tidy facets of the debate seldom seen. As I have limited shelf space and unlimited hard-drive space, I would prefer to see the underlying texts scanned, searchable, and added to Gutenberg as so much else now has, but authors like her are a start. It is also useful to note, however, that most people of the time did not have fingertip access to their period documents either, but rather formed their opinions from what they had readily available. That is one reason I put almost as much stock in Cicero, Aristotle, Blackstone, Locke, the Federalist/Anti-Federalist papers that we have evidence people read and quoted as in the debates themselves which few people were present for. I would also potentially ascribe waxing and waning of the debate in our culture to the temporary disappearance of those texts from popular access. Who the hell read Blackstone or Paine in the 1970's?