Truthfully, I think it depends heavily on the context and how you use that emotion.
The traditional definition is associated with envy, something that is typically negative and jealous IS typically negative.
However, if one becomes jealous of another person's life, which is a good and happy life; they use that jealousy to motivate themselves, they don't allow it to eat at them or to make them bitter, but to make their own life good and happy, I don't think it's so bad in the long run. Jealousy can be used as an inspiration.
On the otherhand, I agree with many of the statements above. People often feel jealous when it comes to someone or something that they love and DO allow that emotion to eat at them and make them bitter.
How many times have you seen a couple fighting over, "You were checking her out!" "No I wasn't!"
But, jealousy is natural and necessary for the human condition.