Which poster went wrong and where?

Here is the following transcript from a thread on another site. Some of the messages have been reposted in in a logical sense as it was a fast and furious exchange, but the statements are direct quotes. :

OP: (Photo of a young male holding a burning American flag with the attached message): “Burning the American flag doesn’t make you a protester IT MAKES YOU AN ASSHOLE.

Person A: What if it is being burned because it is worn out?

OP: That’s a good point but that’s not what this guy is doing

Person A: (OP), I realize that. Until the US First Amendment specifies that national flag-burning is illegal, then it is what it is. Name-calling does nothing but knock the person doing it down the respectability level a notch or two. There are more important battles to fight right now in the US.

Person B: People burning out of malice our lack of respect, should be hung by an American flag!

OP: I agree! (Person B) for president

Person A: (Person B), That would be a violation of the American national flag code, not to mention a plethora of other issues.

OP: Simmer down now

I’m Person A. I honestly tried to keep the conversation objective, but obviously failed miserably. How could this have better been addressed?

Be honest based upon your experience. Would you have just let this go if a good friend was the OP? Possibly addressed it privately instead of publicly?