I don't buy the idea that he's a simple parasite. His biotechnology points otherwise. He has knowledge of his actions, and he questions their validity at Terra Tower. Is that not he asking if one must destroy another's planet in order to survive? He is wondering why that must be, why life only comes from destruction. He is, biologically, a parasite and destroyer, and seems very much to be conflicted about that. That makes for a rather complex personality. I think most of his race don't give it a second thought. But he was destroyed (or almost so) in a counterattack by very strong heroes defending their home world, and that probably made him think if he is justified in killing such as they. Moreover, Schala's connection to him likely gave him an understanding of a conflicted human psyche, and gave him further reason to ponder.
However, it is rather difficult to say that he was corrupted by humanity. It is supposed in the game that the reverse is true - that humanity was tainted by this extraterrestrial source. As such, it would be rather difficult to be tainted by that which is only tainted because of him.
You know, Lavos' conflict is really the same that humanity might face. I rather think he is supposed to be humanity, or a human, writ large. After all, humans must eat and damage the world around to survive. Where is the justification for this? We ask ourselves this, and so does Lavos. He has, I think, become disillusioned with who he is - at least in Cross, he has. Perhaps, even, he has been driven mad. I am certain the creature is conscious and intelligent in Trigger. The only question is, I suppose, his evil, especially if you consider him a larger version of humanity, and how we deal with our environment.
