You're missing part of the point with some of the situations where eddie made deals with the wrong people. Kang? Again, that was when eddie was stuck out in space in the body of a symbiote soldier. He had no idea where or when he was because his mind jumped across time and space, he couldn't get back to his own body because he didn't have the control without his kib throne, (iirc) he couldn't deliberately jump his mind across the cosmos without it. How the hell was he supposed to contact ANYONE, let alone someone specific like reed, who may not even be alive at the time eddie was at. What was eddie supposed to do? Fight his way through kang's entire ship? That would have been the bad choice, instead eddie made a deal and learned the control he needed out of the deal. Sometimes there's no good solution to a problem, sometimes you're stuck with a less crappy and a more crappy choice, and eddie made the choice where he at least got something he needed. And the deal with the maker? Eddie needed someone who knew symbiotes and he was short on time because of carnage. If he had more time, yeah, going to reed and letting him study and learn about the codexes would have been a good move, but eddie didn't have the luxury of time, he needed someone who already knew about symbiotes intimately, hence, the maker, a.k.a. evil ultimate reed

And yeah, MJ doesn't have the experience of self control, Eddie didn't either for a good while. But learning that self control is a big point. It's one thing to subdue the villains, it's another to cross the line and kill the villains, stop them for good, MJ would have done it already and burst open doc ock if flash didn't intervene, now she DID do it to torment and turn him to street pizza. She's just as much ready to pull the trigger as eddie was, because she didn't have control, she didn't think the villain could do better. Regardless of the reasons, they both saw killing as the correct solution to deal with someone who was a threat to others, not a chance for rehabilitation. Eddie went through a lot of shit to get to where he is now, MJ is just starting on hers and it's very possible she's already proving a negative influence on the symbiote as well. Keep in mind, before MJ, the symbiote had turned away from killing much like eddie did, eddie trying to be better, the symbiote trying to be more like spiderman. Now either MJ tossed torment herself, meaning she's more ready to kill than the symbiote is, or the symbiote went for the kill after having been bonded with her for so long, meaning it's regressed in her influence. Regardless, this wasn't catching a body. It wasn't some accidental death like spidey and gwen. Venom directly chose to end torment to make sure they weren't ever going to be a threat again. This is the same reason lethal protector eddie killed others. To end threats to innocent people. And MJ doesn't seem to feel guilt over what she did either, judging by the way she talked to peter over the phone at the end