Telling people that our flag "drips with blood" isn't a good way of convincing them to give one's opinion a hearing. If he has to demean our flag to make his own look good, he's lost the argument already.
There certainly was a connection between slavery and the American flag, or the French or Spanish or British flag for that matter. But as we've grown and changed, though, we've added new stars to the flag, and also changed what it represented. Does the Stars and Stripes flying at home or abroad now represent slavery? Don't you feel uncomfortable or embarassed posting such a claim in time of war?
The Confederate flag hasn't been able to disassociate itself from its unfortunate connection to racialism. In part it's because the Confederacy was defeated and Confederate history stopped, but the Confederate Battle Flag also became a symbol of segregation and White supremacy, so naturally many people are hostile to it. If you want to try to redeem that flag, give it a try, but it will take a lot of effort. Don't assume that that redemptive work is unnecessary or has already been done.
Check out some of the webpages the article you posted linked to. It looks like they are convinced not just that fallen Confederate soldiers deserve respect, but that the rebels were right, and that they were fighting for "our" liberties. Some even advocate secession today.
There's very little serious reflection on slavery and what it meant at the Confederacy Project. The "slavery" that concerns the website's owner is federal taxes and regulation. The condition of slaves a century and a half ago doesn't seem to bother him much.
Intelligent and responsible spokesmen might be able to make a good case for the Confederate Flag flying over Civil War monuments and battlefields, but the net effect of many of those working for that cause is simply to drive people away and convince them that the other side is right.
As for our own flag, think of the reparations controversy. Some measure of "reparations" were paid by those soldiers who fought and died to end slavery in America. There are all the little loopholes: they didn't go to war to free the slaves, the war itself couldn't free all the slaves, some slaveowners fought on the Union side, etc. But even taking that into account, a lot of men gave their lives for the end to slavery, and this, together with later efforts to achieve equal civil rights has helped to redeem our flag of some of its historical associations.
By this point in time, our flag represents people who opposed slavery and felt it wrong and regret it in more than a perfunctory and backhanded way far more than it represents slaveowners. I'm not so sure one could make the same statement about the rebel banners. In any event, insulting the national flag isn't the right way to proceed if you want to convince people.
free dixie,sw