It depends on how you look at it. From a purely scientific point of view we are merely doing our job. Dominant species facilitate change by causing extinctions thereby heralding their own demise only to prepare the ecosystem for a new wave of creation. Basically, we are doing a great job at returning the earth into a primeval state by eliminating all large creatures, essentially leaving only jelly fish in the ocean and insects on land. While we have the capacity to understand this process as individuals, on a species level we are unable to stop this process because we are in competition with each other. It's known as 'the tragedy of the commons' (If I don't catch this fish, somebody else will).
I think it's also important not to fall into the misanthropist trap ("humans are the cause of all the planet's problems") or the fallacy of perpetual natural harmony (i.e. if it wasn't for us stuffing things up). It's an illusion as every species goes extinct sooner or later. We are merely speeding up that process.
From a personal perspective I am totally with you and I often despair at the things I see. As a marine ecologist, I am confronted with the growing threats to our oceans on a daily basis and the future is indeed grim. Not for the planet though, just for us and the species we are affecting negatively (jellyfish probably think we're fantastic!).
But whichever way you look at it, the writing's on the wall.
