I can appreciate humor in science fiction when it's used as comic relief in an otherwise tense story. I'm not as tolerant toward sci-fi comedy, though there are some exceptions, like Red Dwarf. Science fiction requires a willing suspension of disbelief, and if the humor is not done well, there's the risk of the audience laughing at the production instead of with it. Star Trek was always uneven with its light-hearted scenes. I don't know if the fault was in the writing, the direction, or actors' performances, but they often had trouble getting it right.