I haven't read the whole arc in a long time, so forgive me on the details.
What I meant was that 'Bob' was 'good' in that he was a lesser of two evils. If his goal was to save the human race, sacrificing a few individuals and some remote regions might been acceptable as ends justifying the means. And as an AI, I doubt he has the capacity to consider (or conceive of) the morality of such a line of reasoning.
I agree that the symbiotes are parasitic in that a human host doesn't depend on them to live, but are "symbiotic" (for the lack of a better word) in that they give benefits to their hosts. That is apparent more in the older 80s&90s Venom appearances/story/arcs/whatever. But I suppose ultimately the individual symbiote is really what defines it. The Venom symbiote wants a shared relationship from its host, while the Carnage symbiote is exploited almost parasitically by Kassidy to keep him alive (as you said above) and create further mayhem in his killing sprees. The Venom clone seems to have an outright parasitic mind set in regards to it's host. This could be a result of it's youth, as it was created in a lab lacked any sort of 'social' interaction to teach it how to bond with a host, similar to the problems that Toxin and the life foundation symbiotes experienced controlling their immature symbiotes. Or maybe it was genetically altered or psychologically traumatized in the lab to increase it's aggressiveness.
But I would have loved to see the army of Venom clones. Would have been a great (re:better) way for the series to end.