I haven't played Starbound in a while, so when I went back for another round, I was a little surprised to discover that A: new characters share the same universe as old characters, meaning the storyline NPCs are already unlocked in the ruins, and B: you can no longer randomly murder NPCs. I was really hoping there would be a key modifier, like a "force attack" button, as is common in other games that initially disallow casual violence. But I guess there isn't. And as of this writing, I can't seem to find any mods to that effect, either. Here's hoping someone does something about it. it's a real buzzkill. (...or rather, a buzz-no-kill.)
Being unable to commit casual murder or genocide is simply unfitting in a game of this style; a massive sandbox. Personally I agree that a sort of "safety switch" that would allow you to turn on/off friendly fire would greatly improve the game; people who want to play the hero (or just not get swarmed by villagers/accidentally kill a valuable ally) could keep "safe mode" on and people who want to play the villain or just want to add some realism to the game can turn it off. Perhaps there can be a third mode that makes it so you can kill anyone except crew members. Like "Safe, Semi, Full" modes. Maybe said "semi" mode would also keep you from killing vital questgivers, while "full" let's you kill everyone in a "screw the plot" sorta way.