I literally am citing comic runs and eras of the character, you have done nothing but make things up. Venom also wasn't around much in the 80s considering he debuted as a full character in summer 88.
He doesn't eat bad guys, he did that once or twice, mostly it was a threat, it was no on purpose, which you would know if you read anything on the character. The only person he's ever stalked was Spider-man, and again, he only did that briefly, his intial appearance, the one that came right after which he explicitly didn't kill spiderman and led into maximum carnage later, and the one that l mentioned where Spiderman saves Anne and Venom leaves for CA for lethal protector. That's maybe 30 issues or so of being a "bad guy" he doesn't eat anybody in those issues, he only ever does in the later runs, and i t was not intentional.
You are saying that if a character changes fundamentally they are always bad, that makes no sense. If that were true Deadpool, Prowler, Rogue, etc would all still be evil. Characters like Magneto wouldn't have arcs, etc.
No, explicitly he only wanted to kill carnage, they get Venom from his tropical island where he planned to stay to get him to help kill carnage because he turning all of new york into a blood bath, he explicitly stops trying to kill spiderman while cat puts aside her hatred of him, to go kill carnage because he's murdering hundreds every day. He never wanted to kill anybody else, he makes a comment about not letting anyone get in his way, but he doesn't act on it. In fact, during his first appearances, he resents killing anyone who isn't spider-man, even if they're in his way.
Sand man was a good guy for a long period of time until editorial stepped in, Venom is a different case because he's not been a villain most of his career, from 93 to 2000 at least, he was only a villain for his early life when he was debuting in the spiderman book. Once he goes to california he doesn't want to kill spiderman anymore until the sinister six book in the early 00s, and shortly after he auctions the suit. Eddie has literally been a hero/anti-hero longer than he was ever a villain unless you only watch SM3 and some of the cartoons.
He didn't, he tried to and the sinister six thought he was too unstable and crazy to use, they might've briefly used him as a diversion to kill spiderman, but with intent to kill him after he was never a part of the official group. Again it was that short run in the 00s that didn't go anywhere, that hardly undoes the hundred or so issue run before that where he was protecting the homeless in LA.
This was because Eddie as an antagonist for Spiderman never made any sense and editorial never addressed it, so because Eddie being a bad guy didn't work the idea was to get a better suited host who actually had a reason to hate spider-man to be Peter's reverse flash. Every time they tried to make Eddie act like a bad guy fans hated it, and people who "liked it" didn't read the book. The result was a bunch of hosts like Gargan or that one mob boss's kid getting the suit, and eventually having it end up on Flash.