What is King's tone in the opening paragraph? How much you make an argument for its being ironic?

King begins his letter in a sarcastic manner. Irony can be found in the fact that the letter was written from the Birmingham jail.

If I sought to answer all the criticisms that cross my desk, my secretaries would have little time for anything other than such correspondence in the course of the day, and I would have no time for constructive work. But since I feel that you are men of genuine good will and that your criticisms are sincerely set forth, I want to try to answer your statements in what I hope will be patient and reasonable terms.