First off, before all of this happened this site was not nearly as anti-black as it is right now, and what you really mean by "these people" are "some of these people." In fact, one person you argued with is black himself. That's the thing about this site, it's not a hugbox. You will run into people who don't agree with you on a great many things.
> Even before the rioting and looting
To this, I'd say, "before the rioting and looting now, or ever?" This sort of thing is a reaction to a pattern of behavior, not a single behavior in particular. We can go back to well before even this site's existence to see the exact same behaviors, the Ferguson riots for a more recent example.