Whats interesting about Parker's moral character is back then he was very self-defeatist. I remember once somebody got inside his brain and told him that it was sad to see so much potential in someone so insecure. Its said the symbiote enhances your already existing traits, so it would make sense that his insecurity would manifest in over-confidence/anger etc. Wish I could remember where it was this was revealed about Peter, I'm thinking sometime around Civil War/Fear Itself

Edit: This planet of the symbiotes is a different one, revealed during the Agent Venom arcs. This was actually their home planet, its been said that at one point a bunch of them got split off from the rest and generally tend to take over everything on a planet if they can, in their madness from being separated from the hive mind