Source: quora.com

Chapter Eight: Guardians of the Galaxy

Around this point, Iron Man had left the Guardians of the Galaxy and the team needed an Avenger on staff.

So Venom and Captain Marvel took that responsibility. In this time, Venom found his way back to Klyntar, his homeworld, where the other symbiotes finally taught it to not want to kill people all the time. For a time. Before it got that bloodlust back. During this time it developed more of a hulking appearance, becoming the main muscle of the team.

But Flash was still able to keep a pretty good handle on its needs and desires. Flash and the Guardians were drawn into, you guessed it, another Civil War, this one between Captain Marvel and Iron Man over a precognitive Inhuman. The Guardians got involved and wound up on earth. Hey, remember how Flash was given the symbiote by the United States Government?

Well they kind of wanted it back. And they stripped it from him, robbing Venom of the best chance he ever had to be a hero.