If I decide to change my basic worldview from cynical to optimistic about the future of humanity, because I don't think it makes any difference to the world at large what I personally think and it's more fun to be an optimist, is that inherently oxymoronic?
Further thoughts on this topic of what exactly is the influence on the future of humanity of how individuals think and consequently act. If we assume that the future is a bleak war for basic resources unless humanity as a whole changes our impact on the environment, and that the only way to change that future is to change the way most people think about the world, then the way people think is critical.
The current trends in shaping how people think about the world and the environment lean heavily towards terrifying us about the impact of not changing. This tactic works only if people actually respond to the negative message and start thinking and acting differently. On the other hand, if the natural optimists simply choose to believe that "someone" will come up with a "magic bullet" solution to the environmental ills, then optimism is a bad thing as the desired behaviour change will not happen. And therefore optimism can actually contribute to our ultimate demise.
So really, I'm back to square 1; cynical vs optimistic, no clear answer, but optimism does feel better from the inside.