Due to his support of the women’s rights movement and advocacy of social issues (particularly the Ashio Copper Mine Incident), he was jailed.

In 1901, Kinoshita joined Abe Isoo, Katayama Sen, Kōtoku Shūsui, and Kawakami Kiyoshi in founding the Shakai Minshūtō (Social Democratic Party).

In 1904, Kinoshita wrote articles critical of the Russo-Japanese War, and in 1905 unsuccessful ran for election.

After the Heimin Shimbun was suppressed by the government, he began to write for the Shin Kigen Christian-socialist magazine.

He continued to write pacifist and socialist themed novels for the remainder of his career and in his final years was attracted by attempts to form a union of Christianity with Buddhism.