What is one claim opposing King's work to which he is responding in the first paragraph of the letter? To whom is he responding?

The “Letter” is dated April 16, 1963, and addressed to “My Dear Fellow Clergymen.” Dr. King explains that he has read the recent statement published by clergymen in a Birmingham newspaper, describing Dr. King’s recent activities in the city as “unwise and untimely.” Though he does not usually respond to criticisms – he receives far too many for that to be practical – he believes these men are “of genuine good will” and hence do their criticisms deserve an answer (169).