When I saw the meme, I thought it meant that those who protest the US flag because of racism are misguided because the US, under that very flag, has actively fought *against* racist regimes. And while it's overly simplistic (what meme isn't? that's kind of the point of memes) and minimizes the systemic racism that is still very present in the US, I can get behind that general idea - unlike the others, the overall cultural and political arc of the US has continued to bend away from racist policies and practices rather than towards.
However, in order for that meaning to be accurate it must be true that the Confederate flag is one that represents racism. This idea is not exactly a popular one in the politics stream (which is decidedly right-wing), so I thought it could use some clarification.
It was also a bit of a derisive retort, but more along the lines of, "So you agree with me (a guy who's on the left-ish side of things) that the Confederate flag is racist. How's that feel?"
For the record, I'm not a fan of protests against the flag because of racism. The flag (and the nation it stands for) is not an enemy of equality. It is a behemoth that takes a really long time and tremendous effort to turn around, but it is turning.