The author of the letter "Better to stay home than dis the flag" obviously does not understand the foremost point of the protest by teachers in Tokyo and the rest of Japan.
The issue is not about "dissing" the flag. The flag is just an object with no inherent importance. The issue is about the government of Japan forcing teachers to act against reason as instruments of the government's plan to resurrect nationalism and blind devotion to symbols of that nationalism (the flag and the Emperor). This is both dangerous (Japan tried this before and it led to "the Great Japanese Empire" and World War II) and it is unconstitutional. The Tokyo metropolitan government is completely disregarding the teacher's and student's rights to free speech and thought as outlined in the constitution, and illegally punishing teachers with fines and suspensions.