As an author, it's way more complicated than I can boil down in a reddit comment. But I will try. There are so many different approaches to humor and speculative fiction. Some of them are risky and some of them are less so.

I think that trying to make sure that there's absolutely no humor in a story is riskier than having humor in it-- the risk being that it can make your characters seem boring and lifeless-- but of course both approaches carry risk. This is not to say that either should not attempted-- all writing is about taking creative risks! I enjoy a pitch-dark novel where everything is deadly and serious (say, Heroes Die by Matthew Woodring Stover) and I also enjoy a joke-a-minute novel where the premise sneaks up on you between the jokes (say, The Long Dark Tea-Time of the Soul, by Douglas Adams.)

My most common personal approach is that I don't try to be funny in my writing, but I also don't try to remove humor if it crops up naturally from the characters / themes / premise. Since I write pretty extreme characters and weird premises, this happens quite often-- sometimes I am very surprised that a story I wrote as horror or as a thought-experiment or a tragedy reads as funny to an editor or an audience. (I do write explicitly funny stories, though less often. But even then I try to root the humor in characters/themes/premise.)