It's easy to dismiss cynics as little more than an irritating trolls, but I would argue they have their value.
The typical cynic questions everything and rarely accepts new ideas or pathways at face value. While this is tough for those already on a proven path, it's often helpful to stop and ask those same questions. If the answers are all good, power on!
Reminds me of cut once, measure twice. Even if you're sure.
As one who suffers from a case of relentless optimism and can-do-attitude, cynics can balance out the scales by challenging assumptions, and helping people like me take a short breather to ensure decisions are based on realistic expectations.
I think where we cross swords is when neither side of the fence feels they can accept any help or guidance from their opposites.
As with both cocktails and endeavors by reasonable people, moderation is the key to success.