It's not inconceivable that an advanced race will destroy each other but I think that sentiment underestimates people's selfishness. Take the 1960s, everybody thought the US and USSR would blow each other up, but their selfishness outweighed their lust for domination enough to keep from taking any action that would cause their own destruction.
The more likely extinction is the 'death by 1000 needles', like the gradual destruction of the environment where by the time we can personally feel the effects, oops, too late.
People who wake up with a sharp horrible pain in their stomach go straight to the doctor. People who gradually get more and more minor symptoms ignore it and ignore it until the cancer has metastasized. For the same reason there probably won't be any flashy sudden man-made extinction, but might be a gradual negligent man-made extinction.
But this is Star Trek, and the premise of Star Trek is that the future is better than the past. So why would you bring it up in a Voyager thread?
I don't have a problem with the planet advancing that much in several hundred years. They seemed pretty 1500s pretty early in the episode. What I have a problem with is that, after Jin said "We're not ready to join the rest of the galaxy yet", a few seconds after ships didn't emerge and say "Okay, we're ready!"