I wouldn't go so far as to say we're a plague on the planet. Sure, we produce toxins and kill animals, but many animals would be dying off anyways and evolution creates new bacteria to eat the toxins. I remember reading something on /r/science about bacteria being discovered that could digest plastic and have organic waste. The fact is that nature is amazing. I really don't think humans are advanced enough to make a huge impact. Eventually we're all going to die off and nature will turn everything we've made into dust. I was watching discovery and it said that in as little as 1000 years all of our modern buildings and bridges and machines would be gone. No trace. The pyramids will last longer than all the industrial stuff we've built and that's only because they're made of stone.

All in all I wouldn't give humans enough credit to be called a "plague." I think we're just here for a small time and eventually we'll be gone. Sure, we have the power to change things. But even if we happen to destroy something, nature will fill the gap. We couldn't beat it if we tried.

*I am not defending the killing of animals or destruction of nature, just commenting on my opinion of human impact.