Star Trek is "soft" because it doesn't pay much attention to plausibility. Warp drive and transporter beaming aside, things like splitting a person in two to make a Jeckle-Hyde pair, pixie eared aliens who look just like us but are based on different biology yet can breed with humans, FTL telepathy, and the sequel series' endless parade of ____yon particles of week are not based on much that's scientifically plausible at all. It's not science fantasy, though.
That works for me. I look at it more as a platform for telling good stories in, with a general emphasis on starship combat.
I think it just sort of irritates me that there are so many inconsistencies that ignore the things that were plausible in TOS. What was worse was when those inconsistencies became the formula.
One of the things that made Dune and Ringworld so great was that they laid down the rules, so you can really get a good picture of what is and is not possible in their respective universes.