Lu Xun lived in China and during his time, people that gathered enough nerve to rebel against the powers that be were socially martyred, and if they had a political career, it would be rendered nonexistent if they went against their party lines. So dissenters had to tread carefully and be creative whenever they spoke out so that they could keep their livelihoods and still express themselves. Thus, the crazy label works out rather well for Lu Xun; now he can express his dissident views, through the Madman, without any backlash from society because his character is already mad.
"ANYTHING TASTES GOOD WITH A LITTLE SALT AND PEPPER: CANNIBALISM IN LU XUN'S "DIARY OF A MADMAN","
The Corinthian: Vol. 7, Article 11.
Available at: https://kb.gcsu.edu/thecorinthian/vol7/iss1/11