Like I said, humans have had a big impact on Earth. No argument there.
There were also thousands of homo erectus and homo habilis individuals that were clever enough to use tools and adapt to new environments. They're a part of the process of coevolution between people and technology that we are still experiencing. That's why we're special, that process. The process will end at some point, and that's ok.
There are people in this thread that think their lives are meaningless if they don't leave some irreversible mark on the fabric of reality. I don't think that's a reasonable perspective. I prefer the perspective of an intelligent ape. Intelligent ape is excited about smartphones and antibiotics, even if the Earth is doomed to be swallowed by the sun.
I think you missed the point here. This shooter had no opportunities prested to him. He wasn't smart enough or connected enough to ever be comfortable, let alone actually do something noteworthy. Being on the news for a day or two is the only "fantasy" he could possibly achieve. It not about causing a sea-change, it's just about getting noticed.
He wasn't born a monster, but violence was the only obvious route to having any impact on his surroundings.
American society loves guns and hates helping poor people, this is what we get.