"Assuming we find lots of life (modest assumption!), we do have the ability to become like a cancer to that life. It's not a trivial question to be dismissed out of hand."

Or they (alien life) could be a cancer on our culture.
I agree, it's not a trivial question. But I think we *might* be capable of handling the situation.
Life isn't "safe". If we stay on this planet long enough, one thing is a near certainty, a big rock will land on our head, killing lots of people and lots of other animals. And in order to survive from that "ordeal" caring for the welfare of whales and spotted owls will probably not be the highest priority.
Let's find this alien life before getting all excited about "solving" that problem- it could take centuries before we are faced with the problem.