This is an alien creature than concealed its true nature from Peter for weeks (meaning that Peter didn't even know it was a living being for most of its time with him) and was taking over his body for joyrides, depriving him of much needed sleep. When Peter discovered it was alive, the symbiote tried to forcefully bond with him and restrain his movements. And then it bonded with Eddie Brock for the purposes of terrorizing and killing him.
So why do some fans say Peter was wrong to reject the symbiote?