I feel that Rustin's story is a sad story, about a radical who's increasing disillusionment with the left lead him further and further right throughout his life, to the point that Ronald Reagan praised him upon his death. He ended up as a liberal hawk in the Scoop Jackson model: professing social democracy and civil rights at home, and imperialism abroad.
For christsakes, he supported apartheid South Africa (and its comprador allies) against Angola just because Angola and the MPLA got military aid from the Soviet Union and Cuba. Anti-communism is a poison.