I had to stop reading.

Most of what I'm about to right is my observations and opinions- neither right now wrong. Please read openmindedly.

Venom became a villain mostly because of Eddie Brock and his animosity toward Spider-Man. The rest was because the the sustenance that the symbiote required to survive (later replaced by chocolate).

It's been a while since I've read the originals, but if I correctly, the symbiote itself was rather neutral, but enhanced emotion (although it seemed to be particularly the negative emotions). When Peter acquired the symbiote, he was dealing with a lot of negative emotion, which the symbiote enhanced.

Was the symbiote bad because of Peter? While Peter was the host filled with negative emotion, yes. It became even worse with Eddie because his emotions were significantly more negative.

Did Peter make the Venom a villain? No. Not even possible. The symbiote never became Venom until merging with Eddie Brock. Furthermore, the symbiote had its own personality before ever reaching any of its' Earth hosts.