In some ways, this is an opinion, so I'm not 100% sure I will agree with your teacher. But in my opinion, the conflict is between the speaker and himself. I think it's an internal conflict between the parts of him that are optimistic and pessimistic.
I think you can see this in the way the essay unfolds. He talks first about all the problems there are. He talks about the pollution, and he talks about the idea that there will always be a need for prisons. And even when he starts talking more optimistically, he still keeps saying "if."
So I think that different parts of him are disagreeing. One part wants to think things will be okay, but the other part sees problems.