Allen says people who support flag burners might "note an irony in my argument" (lines 39-40) explain what allen means, using details from the editorial to support your answer

The dissenters in the flag-burning case and their supporters might at this juncture note an irony in my argument. My point is that freedom of conscience and expression is at the core of our self-conception and that commitment to it requires the rejection of official dogma. But how is that admittedly dogmatic belief different from any other dogma, such as the one inferring that freedom of expression stops at the border of the flag?

The crucial distinction is that the commitment to freedom of conscience and expression states the simplest and least self-contradictory principle that seems to capture our aspirations. Any other principle is hopelessly at odds with our commitment to freedom of conscience. The controversy surrounding the flag-burning case makes the case well.

The controversy will rage precisely because burning the flag is such a powerful form of communication. Were it not, who would care? Thus were we to embrace a prohibiton on such communication, we would be saying that the 1st Amendment protects expression only when no one is offended. That would mean that this aspect of the 1st Amendment would be of virtually no consequence. It would protect a person only when no protection was needed. Thus, we do have one official dogma-each American may think and express anything he wants. The exception is expression that involves the risk of injury to others and the destruction of someone else`s property. Neither was present in this case.