In the U .S., Science Fiction is a sub-genre with a whole of lot socialists, S. Brust, Terry Bisson, Kim Stanley Robinson, Maureen F. McHugh, Gregory Feeley, Eric Flint have all explicity identified themselves as socialists. Also I can think of a number who are at least left-liberals completely devoid of market worship the late lamented Octavia Butler was at least radical if not socialist. Charles Stross. Cory Doctorow, John Barnes, (It would not surprise me of Corty Doctorow had actually used the S-word, but I canotn find anything offhand.)
I guarantee that I've left out many times the number of socialists I've included, not mention the more or less radical non-socialists.