See, that's just it - I've heard that was added in after the fact (or in an adaptation, I forget) to to justify Peter's rejection of it. Originally all it was doing running around as Spiderman at night and he rejected it as soon as he found out it was alive without stopping to think or attempt to communicate. There's a pretty good run down of it here. Of course each new adaptation ramps up the hostility of the symbiote even more.
Nah. I was reading Spider-Man at the time, and the writers definitely wrote in that it was taking control of Peter's body
and making him more of a loose cannon. Going to sleep at home, in bed, and waking up on the side of a skyscraper wasn't just written for the movie... that's comic-canon, too. It wasn't just that it was alive, but that it was gradually trying to take over his body that made Peter try to get rid of it.
Wiki description of the events:
Writer Tom DeFalco and artist Ron Frenz subsequently established that the costume was a sentient alien symbiote and also that it was vulnerable to both flame and high sonic energy during their run on The Amazing Spider-Man. It was in that storyline that the costume would envelop Peter Parker while he slept, and go out at night to fight crime, leaving Parker inexplicably exhausted in the morning. Parker had the costume examined by Reed Richards, who discovered that it was alive, and when Parker realized it was trying to permanently bond to Parker's body, he rejects it, and it is contained by the Fantastic Four. The Symbiote escapes and attacks Parker, who uses the sound waves from a cathedral's church bell to repel it.
When combined with Eddie Brock, who already had a significant (one-sided) grudge against Peter Parker (and was already a bit mentally warped), it became decidedly unhinged, since both symbiote and host wanted to kill Peter at that point.
Over the subsequent story arcs, it's been established that the symbiote is amoral at least
, if not outright pathological. While being worn by Mac Gargan (Scorpion), it more or less took over for large portions of time, and had Mac engage in cannibalism (something that Mac, as vicious as he was, wouldn't have done by choice).