Sci-fi gaming is hard. one big reason is because there really aren't any cheat codes (i.e. magical spells) the universe of a Sci-fi campaign is limited by a facsimile of known science, fantasy gaming doesn't generally have this issue. Beyond the investment in universes fandom cliques have latched onto over the years and the problems that can create sci-fi gaming has other issues.
With rare exception a fantasy universe isn't undo on the first appearance of a fairy, demon, vampire, or orc; should something new show up in a sci-fi universe you've got some explaining to do and the explanation should reasonably mesh with how the universe works.
My last post on transporters being B.S. touched on this; a sci-fi setting needs a coherent and moderately consistent framework on how things work. Sure science makes new discoveries all the time and technology improves all the time but some things just don't change. A lasers are light, they are limited to lightspeed, everything in the universe is effectively limited by the speed of light even cheating with whackeyon particles and hyper/sub space doesn't change this.
The universe is big, really big. The vast size of the universe in a sci-fi setting not bound to our earth is a pretty serious affair. There are very few fantasy camapigns where folks can jump in a ram ship get the sucker up to 99% the speed of light and go as far as they can for 10 of their own years... most of us lack the handle on math to even say how far they'd actually get in all that time (it's really far but not far at all considering how gosh darn big the universe is).
If the tech in your sci-fi campaign doesn't pay attention to what it is enabling any devious band with resources is goign to inflict havoc on the universe of that campaign. If nuclear powered starships common in your campaign, well the players have a dirty bomb they can use in a desperate situation, it get's even worse with exotic fuel systems. If there are disintegrators in your campaign every barrier, every target is getting a big hole punched in it and the GM is ultimately goign to have to unrealistically restrain the use of such items. Teleportaion works... be sure how and pay attention to what you are doing or the universe is going to shrink even more. If food replicators work for a wide array of races... well, you've handed anyone really bright and talented that can operate one the means to create a wide array of poisons, acids, and explosives with careful menu selections.
Sci-fi gaming is hard because all the pieces interact with each other with a great degree of verisimilitude and hand-waved logic or lapses of logic can wipe away the universe and ruin a campaign.