It is never easy to assign the values of good or bad to any particular behavior or belief. What may be seen as a bad principle today may turn out to be beneficial hundreds of years from now. In this particular case, being cynical is not necessarily good or bad in an immediate sense. One person could view a politician's actions as altruistic, while a more cynical person may see the exact same actions as self-serving. Both points of view may be considered valid until history bears out the true facts.
The problem with being cynical is the same as being too skeptical, pragmatic, stoic or analytical. Holding too tightly to one particular philosophy or moral structure may not be the healthiest way to approach life's constant changes. Being too cynical about the motivations of others can lead to a life of total distrust and bitter disappointments. Every once in a while, an act of kindness or philanthropy or charity does happen for altruistic reasons, so being too cynical to appreciate the essential goodness of others can be socially crippling.
There is such a thing as a healthy level of cynicism, however. There is an old saying that a pessimist is rarely disappointed, and the same philosophy holds true for the cynical amongst us. A cynical investigative reporter, for example, may have enough distrust of government institutions to hold government officials accountable for their actions. Many job applicants must be able to impress the most cynical member of a committee before landing the position. Being cynical, at least in the healthiest sense of the word, can actually be an asset in certain occupations requiring a critical eye or a sense of discernment. Simon Cowell, the ascerbic judge on American Idol, may be cynical about the music business, but his cynicism does allow him to recognize true talent.
In general, however, it is rarely good to be viewed by others as completely cynical. The word "cynical" is almost always bundled with other negative qualities such as bitter or angry. A little cynicism often goes a long way, much like sarcasm or pessimism. Eventually others may anticipate a cynical response and avoid the risk of engaging in conversations altogether. Being cynical may work as a defense mechanism against those with truly self-serving intentions, but this lack of trust may also cause a cynic to miss out on some of life's pleasures as well.