The reason they killed Loki in the first ten minutes is because Loki absolutely would not have hesitated to kill Vision, or steal the time stone.
Avengers: Someone’s killed Dr. Strange and Vision!
Loki, admiring his new necklace and glowing yellow paperweight: Tragic
Wanda: if we destroyed the mind stone it would kill Vision D:
Loki, already stabbing him: oh no
Thor: Hey, didn’t Midgard have a wizard around here earlier? Loki, you remember the wizard, right?
Loki, currently garroting Dr. Strange with the time stone: I don’t recall
I CAN’T STOP LAUGHING
Steve: We don’t trade lives
Loki, already trying to pop out the mind stone: who’s “we”