It's not difficult to be dark. Just look around. I mean, really look around. But being dark doesn't make things better for anyone, maybe for you (and I'm not so sure about that). And an attitude like that will piss off more and more people and you'll hate them more and more and the spiral will begin to twist and it'll never end. And then you'll die alone, no big deal.
Positive people live longer, which is natural. But I'm not so sure if just that is enough. I agree with Lad, being positive and good while still being able to 'do what needs to be done' seems like a fine choice for an attitude.