More evidence socialism in science fiction was present long before Ken MacLeod and China Miéville:
MICHELISM (“MISH-el-ism”) At the Third Eastern in October 1937, Don Wollheim read a speech written by John Michel, which denounced the “Gernsback Delusion” and declared that stf had made idealists and dreamers of fans, since it is the best form of escape literature ever invented. Since we cannot escape from the world, science-fiction has failed in not facing the realities being fought out in Madrid and Shanghai [and later in other locations we’ll leave you to fill in as events unprogress] and in the battles between reaction and progressive forces at home and abroad. “THEREFORE: Be it moved that this, the Third Eastern Science Fiction Convention, shall place itself on record as opposing all forces leading to barbarism, the advancement of pseudo-sciences and militaristic ideologies [referring to the racist notions of Naziism], and shall further resolve that science-fiction should by nature stand for all forces working for a more unified world, a more Utopian existence, the application of science to human happiness, and a saner outlook on life.” Hot debate followed and the motion was defeated 12 to 8 (the 8 being the Futurians, voting en bloc).
From Fancyclopedia II, first published in 1959, a large encyclopedia of science fiction fandom and fanspeak. You’ll have to scroll down a bit to find this, as there are no links to the individual entries. Found thanks to mr rasfw, James Nicoll.