Not "everyone was armed" in 1776

That's not the point, it's not about "everyone is armed" but about everyone having a right to be armed.

Mostly just white people who could afford a gun

Similarly, it's irrelevant whether you can or can not afford a gun, many people can't afford a megaphone, that doesn't mean they do not have the right to free speech - the point is that everybody can on an equal terms. You get a megaphone for $20, I get it for $20, whether you choose or are able to spend that money is on you.

Many slave masters didn't want a federal government taking their arms

What does that have to do with anything? The intent of the 2nd amendment is articulated very clearly by the founders (protect against a tyrannical federal government), and it has nothing to do with protecting "the property" AKA slaves or whatever, that's just race baiting and despicable tactics. Do you see everything through the lens of a race? There is a word for that you know ...